Buying snails in central/eastern Europe?

This is not something I'd have expected to be a problem, but I'm having trouble finding a place to buy the snails I wanted. I have a small tank and was planning to introduce a handful of bladder snails, but it turns out... I'm having difficulty finding anywhere to get some. The local aquarium stores I've tried only have ramshorns or assassin snails, and while I've found a few individual non-store sellers on personal ad sites who are trying to get rid of theirs, I'm admittedly hesitant to purchase from complete strangers where I have no info as to what shape the snails may be in. Does anyone know any mostly reputable sellers I could get a small amount of bladder snails from? (Really, 1-5, so probably not worth the hassle for most individual sellers...?) I'm in Poland, but shipped snails could potentially arrive safely from Germany or the Czech Republic or etc. I think?