There is a small not so black market of distributors for these, notably Biore UV which is easily accessible on Amazon - as well as ebay and other ecomm channels.

I fly frequently to Japan, and always stock up on Biore UV, and lately with the USD to JPY, it makes more sense too stock up more. :)

Lots of items from amazon.co.jp also have free shipping to USA, it's nice.

If you can't enter Japan, but still feel the need (it sounds silly, but maybe on layover) you can fly through Haneda which has all shops accessible for transfers. Narita can too depending which terminal you fly in, ANA yes, JAL no.