Man, I feel your pain. It seems the resto catalogs all have the same parts! I couldn't find the dust shield for my 3 spd. Saginaw ANYWHERE! Then, the last place I EVER thought of had it: the local Chevy dealership (and it was affordable {$28.90!}). I checked with all my sources ( Truck, Cheyenne Pickup Parts, Golden State Pickup Parts, etc.) and came up with the same thing you did, NOTHING. Well, I can give you the best advice possible, make friends with the parts/service manager at your local dealership (take lots of donuts) and you might get lucky and he/she will order it for you. I'm sure that there's some type of cross-reference they use to help restorers and such. Oh yeah, and don't let the fool you. I was told over and over again that the dealer doesn't carry parts for vehicles that old, but I don't recall 3 speed saginaws being used today, so how'd I get my dust shield? Hope this helps!
-Mike