I'm based in the UK, I have always ordered bras online, tried them on, sent them back etc.
Recently I plucked up the courage to go and get fitted, I chose a massive department store, called up, explained my situation and made an appointment. They were so cool about it, I thought they had misheard that I was trans and would be presenting in guy (well androgynous) mode.
They were super friendly, understanding and helpful, I was their for almost 1.5 hours, we had a good laugh and I bought 3 bras.
If you're unsure about how the shop will react, chain or otherwise, give them a call or if its a small independent drop them an email.
Most if not all are understanding and by contacting them in advance it means their more likely to be understanding.
I know it shouldn't be that way, but there are some real small minded people out in the world.
Good luck