Since when Stex support margin trading? If OP's looking for altcoin trading site then there's a bunch of them, but even though that is the case, I wouldn't recommend Stex either.

Bitmax also supports margin iirc, and last time I checked they don't require KYC, at least if you don't do a lot of tx.

Seems like margin traders are having a hard time right now if you come from the US. Let's hope Bakt could change that (if they really start in September).