Then there's another way of getting his birth certificate - you can simply request the Polish government to send you a certified copy of what they have on the books.

The issue is that the burden of proof that you're a direct descendant lies on you (which can be tricky if you live outside of Poland). The process costs 22/33PLN and in my experience USC (the government office which handles it) is very accommodating. Here's a very recent one I requested: http://i.imgur.com/wROo5M9.png - I though he died in 1826, but as I got the place and the spouse right they did find him. As you can see the place of birth is missing, but whether it's included is more or less random. You can use it as a backup plan.