Where can I get a u joint that fits a 1985 dodge pickups drive shaft that has a 1995 dodge pickup rear end. Two different size widths and cap sizes

Wow thats a hard one. You are most likely going to have to get it custom fabricated.

Try junk yard

You need a custom part you may need a machine shop to fabricatr one custom for that application.

If you have the 85 and 95 drive shafts have them cut, welded and balanced.

I doubt that any of the chain part stores will have exactly what u need. One of the old school, individual store might or get it fabricated.