I'd hop around on some of the sponsor sites on FTE first. If no luck try Bronco Graveyard, LMC, Dennis Carpenter......
I would really be suprised if you don't find one on this site's sponsor list though!
Boneyard would be a good bet too.
Gary, A salvage yard is probably gonna be the only place to find one, could be wrong. Get one from a pickup and it should work. I would start with the same engine tranny (like 360/C6). You can bend it a little if you need to.
I have a 79 150 with a 302 and a c4. When I take off too fast, well actually it doesn't have to be all that fast at all but the whole shifter will pull down and it will stay in 2nd until you pull it back up to drive. I have been told different things I have been told kickdown is out of adjustment, I have been told motor mount, but it does it without the kickdown even hooked up and it has 2 brand new motor mounts. The only thing I can think is the transmission mount what do you guys think?
Definitely sounds like engine torque is twisting tranny enough to bump shifter down a gear. If nothing is loose or worn at or around the engine mounts, the tranny mount and cross member would be the next to check. Linkage adjustment might be "on the edge" enough that any torque causes the linkage to down shift. When it's in drive, try just tapping the shifter with a finger or two to see if it feels like it just falls into second. If it does, back off the adjustment enough so that just tapping the shifter doesn't cause it to fall into second.