I've tried steeping various berries in vodka, with excellent results - raspberries, strawberries, blackberries, etc. I had one failure, which was melon - it has too much water in it, presumably - it actually went off, in spite of being soaked in alcohol! Strawberries work beautifully, although all the colour leaches out of the strawberries, which end up looking weird and grey, so you'd want to chuck them out once they've imparted their flavour, on aesthetic grounds.
I've also made krupnik, which is vodka with honey and spices - delicious in the winter, served hot! Google for a recipe, I'm sure you'll find one.
I wouldn't worry about finding Polish pure spirit, though you might find it in a Polish deli. That's if it's legal here! I don't think 'rectified spirit' is, deadly stuff that they drink in Poland! 120 proof, whatever that means.
In France they use 'anise' spirit for the same purpose. Any clear spirit will do.