You may be looking for a very specialized item that simply doesn't exist on the market, and may not for years to come. Possibly never.
As anxious for the item that you are and for what you are willing to pay to track it down, I would look into having the item custom-made. I would contact the manufacturer or importer of the Desert Eagle on this to see if they would be willing to do it or would know somebody who would.
Otherwise, if you haven't checked through this list already, as referenced above and listed below, you might try all of them. But to be honest, rather than spend countless hours on the internet and with phone calls, I would look into having the item you want custom-made, although any custom-made major handgun part is by no means cheap.
Numrich/Gun Parts Corp. doesn't list all the parts they have in stock on their website; you might contact them for what you need at email@example.com.
If you still don't have any luck with them try:
Websites that may have gun parts:
eBay (go to GUNSURPLUSPARTS, I think)
You might also find a broken or inoperable "parts gun" for sale on one of these websites, which can be cannibalized for the parts you need. You can sell the remaining parts on the internet, or this forum's host. Re-post here if you aren't familiar with purchasing guns across state lines.
www.brownells.com (parts for certain late-production firearms only)
Bob's Gun Shop at www.gun-parts.com, or firstname.lastname@example.org and (501) 767-1970
Brock's Gunsmithing Inc. www.brocksgunsmithinginc.com Click on "parts"
Out Back Gun Parts (812) 945-0480
www.jackfirstgun.com (605) 343-9544
Rusted&Busted Bob's Box 24 Whitmore Ca. 96096
Western Gun Parts, www.westerngunparts.com/default.htm, 1-403-489-5711 (Canada)
Jim Wisner (206/360) 748-8942 360-748-4590 www.wisnerinc.com (obsolete firearms parts)
Jim Horvath, P.O. Box 791548, New Orleans, La 70179-1548
Ken's Parts and Guns in Irving, TX
email@example.com and firstname.lastname@example.org (Broomhandle Mauser parts)
www.1896mauser.com/index.html (Broomhandle Mauser parts)
http://www.buymilsurp.com and http://www.surplusbunker.com (parts for various imported and military surplus guns)
Glend Arms Mfg. Co., PO Box 361, Secane, Pa. 19018 (manufacturer of firing pins)
Marstar Canada www.marstar.ca (British Commonwealth military arms)
www.coltparts.com (original and some reproduction parts)
www.ssporters.com (parts for old handguns, curios and relics)
Liberty Antique Gunworks, 19 Key St., Eastport, Me. 04631 (207) 853-4116
(obsolete S&W parts)
High Standard parts (203) 239-1012
Hoosier Gun Parts, www.hoosiergunworks.com
Marty's Gunsmithing, 371 Spring Valley Rd. Elko, NV. 89801 Ph. (207)738-2666 (obsolete Remington parts)
www.oldwestgunsmith.com, email@example.com (old handguns, esp. Smith & Wesson parts)
Tom Heller, Heller Arms, Ltd., P O Box 398, St Charles MO 63302 Phone: (636) 447-3006 E-mail: firstname.lastname@example.org
Buckingham's Antique Winchesters, Winchester parts, 501 Eaton Brazil Road, TN 38382, (731) 559-4169
G.S. Armatt,Inc. 335 Gay Road, Zebulon, NC 27597, (919) 269-8449, email@example.com
Earls Repair Service, Inc. , 437 R Chandler St. Tewksbury, Ma., 01876
978-851-2656. http://carlwalther.com (Walther parts and service)
http://www.topgunsupply.com/gun-parts/ (Glock, GSG-5, HK, Kahr, Sig Sauer, Wilson, AR15)
www.bersafirearmsusa.com (Parts for Bersa, Firestorm (Llama) and Comanche (Llama) handguns)
Unique/M.A.P.E 10 Les Allees F-64700 Hendaye FRANCE (Parts for French-made guns)
www.tanfoglioparts.com (Parts for Tanfoglio-made autos, possibly including EAA Witnesses)
www.vtigunparts.com, firstname.lastname@example.org, VTI Gun Parts, PO Bx 509,Lakeville, Ct. 06039 (Parts for Uberti, Peitta, Pedersoli, Ruger, Colt and USFA replica and reproduction guns.)
John D. Bush. email@example.com and/or firstname.lastname@example.org (Magazines and parts for FEG pocket autos and Tokarevs)
Miga Gun Parts, a division of Midway Guns, PO Box 569, 9754 E Oglethorpe
Hwy, Midway, GA 31320, Phone: 912-884-5616 or 884-5597, e-mail:
email@example.com, www.galleryofguns.com, Ask for Penny
Dixie Gun Works in Union City Tenn (Colt and replica handgun parts)
John A. Kopec (916)472-3438 (Colt grips)
Egyption Helwan parts: M&M Gunsmithing (703)739-2150
Old West Parts Bin, 1463 Funston Ave., San Francisco,Ca. 94122 (antique guns)
Stevens Sight & Tool Co., RD 1 Box 307C, Effort, Pa. 18330 (215)681-5670 (Old Stevens firearms)
Ed Cox..Circle C X Antiques. PO Bx 2197, Fernley Nv. 89408 (775)575-6205 (old handguns)
Springfield Sporters, (724) 254-2626, Mon-Fri 0900 to 1700 hrs EST/EDT
http://www.germanguns.de/exportindex.htm (German and maybe some other European firearms.)
PHH,Inc., 1330 Center Ave.,Pittsburgh,Pa. 15229 Ph#412-766-6100 (Ruger parts)
WAFFEN WIESER GESELLSCHAFT M.B.H. at http://web2.cylex.de/firma-home/waffen-wieser-gesellschaft-m-b-h--4384190.html or http://www.steyrwaffen.at or www.cds.ehrenreich.de (Parts for Steyr, and perhaps other old Austrian or German handguns)
www.fultonsofbisley.com or Terry Abram +44 (0) 1245 231753 (United Kingdom) (British Commonwealth guns)
www.thedealershowroom.com (military rifles and pistols)
For more listings go to http://www.brownells.com/categories.aspx?c=4815
Some vendors have a "wish-list" on their web pages....check their site for such a feature and add you wants to it.
Also, try to post on some want ads boards, (gunbroker.com has one as does auctionarms.com) or ask questions at some shooters forums. Search for some here: www.gunshow.net/links.htm
There's other possibilities if you don't have any luck with the above. Re-post here.