You are right, in Serbia is almost impossible to buying some strings what you want
Two weeks ago I was in the biggest musicshop in Serbia...I wanted to buy a 12-56 strings, the seller look at me, like I had ask something punishable
The guy told me, that this thickness had never asked by customers (ok, I belive, Serbia is not a metal country like Sweden, but, it's a musicshop, and it's the biggest...). The thickest strings was the 12-54, and only from the Dunlop. Unbelievable, but true.
I find it hard to buy strings from visiting physical stores in the US too. I end up buying them online.