I have the same trouble as I don't find my sizes at every store. The good news is in a major city like SFO in the USA, there will be big and tall stores, just search for them.

I always worry when checking a bag for longer trips overseas since big and tall stores are mostly non existent. On top of that, larger clothes take up more room which limits how many days you can get out of a carry on. BA delayed my bag last year when going to Bulgaria and all they could promise was next day delivery, but no specifics. Luckily, it showed up next day as promised.

Travel insurance is your friend in these cases, buy what you need and move on and settle it when you get home. I always carry 1 change of clothes in my backpack. Worst case, I can do same day laundry at the hotel and rotate what I wore over and what was in my backpack, and claim the laundry fees against insurance.