Also, as for German uniforms, take a look at
https://www.atthefront.com/ http://www.panther-store.cz/en https://www.1944militaria.com/
Some cheaper/lesser quality/authenticity gear can be found at
http://www.militarytour.com/
People also buy from Asian retailers like HikiShop or Spearhead but I'd stay away from those.
I don't know any sources for Polish repro gear.
You can also check out
http://www.ontarioairsoftwwiireenactors.com/ Register on the forum. There you can get great help in building your impression. Maybe someone can even point you towards retailer that sells Polish gear.