Been browsing the net and came across this site...looks quite good with trail tips in Poland

Best Offroading trails in Poland : Wikiloc

Discopol is your man to ask

just taking a look now but i dont know whether its the choice of google maps to show the routes or the fact that most of them are road routes, i will investigate a little further and see if any of them are worth doing.

Might be time to call in Polish reinforcements in the form of CJ2A he is another Brit living and playing out here albeit in the south.