i've been searching everywhere and I can only find 350s that fit into 1987s, can anyone help me out?

The reason they are listed that way is the 87 was the first year for the 350 in the thirdgen, it also had the canted center bolts for the intake, you can get an 87 350 longblock, but you'll also need an 87 up baseplate.

'87-up doesn't have anything to do with "fit". As 'Racer said, that's just when the factory started offering them in 3rd gens.

There are many options for getting a 350 into your car. '86-earlier will work, too. A 350 shortblock would work under your heads. Etc., etc., etc.