Where could I find a 34 H bra? [US]

I'm willing to buy either online or in person, I'd really like to try one out before I move out. My mom and I have no idea what store would sell that size, the most we see anywhere is DDD. I remeasured myself using the A Bra That Fits calculator, I currently wear a 36 DDD bra, and it told me I'm a 34H in US sizing. I keep on getting told my intense back pain and chest pain shouldn't happen if I had a properly fitting bra, which I doubt since I'm pretty short and oddly proportioned lol. But i figure i may as well try, im desperate to alleviate it right now. So if anyone had any pointers i'd super appreciate it!