NO! Being "able" to BUY in a permitted State means several things (requirements!);
1. You're a Resident and Complying with ALL law's within that States "mechanism" for such licensure; i.e. being "Registerd"; having a CARD, etc.
2. UNLESS "One" wishes to buy from the "underground" market, then all rules are off and legal liability begins; Risk v/s Reward theory.
3. YOUR Brother "could" supply You, however he better know what he's doing before he begins that task. IF you/she were my Sister, i'd help you/her,regardless of "Law"!