So my ex decided to invite me to a disco/70's party at his place and I decided to go as a basketball player with those really small tight shorts and the knee high stripped socks... but I dont know where to find any. Any ideas?

My best source for old clothing for disguises are 2nd hand cloth stores, specially those who aren't labeled as "fashionable vintage shops".
Don't know if you have any there.

Value Village is your friend.

Definately Goodwill or the Salvation Army for the old shorts and the miraculous shirt that is simultaneously drab and gaudy.

The socks are still available at most stores. Just look harder.