It's actually quite hard to get now in the small Warsaw shops
It's never been a thing in western Poland where I am... so Biedronka was the first place I ever saw it on sale. Is kaszanka in Warsaw more with barley or buckwheat?
My favorite kaszanka though was in Hungary where they do two types, blood (veres hurka) and liver (majas hurka) the liver kaszanka is very yummy and the blood version has a hint of chilli and is almost but not quite sweet.
Stores here now have kaszanka with liver (combined with blood) but not just the liver..... : (