(I'm not seeing a link or I'd put it here.) So in summary, there is a Polish name section of this site. Benefits include that the site is in English, and you don't have to know the special characters of other alphabets etc. The site is very simple and also has frequent updates so you'll want to keep checking it out. http://www.locatemyname.com/
Mr Hoffman also recommends these 2 links. He states, "Both have their flaws and idiosyncracies; and both are in Polish."
I find sites like these about surnames helpful tools. I thought I'd test out the site myself. I'm thinking I may have looked at the site a few years ago and that there is much more than the last time I looked. I know Sanetra is not that common of a surname, this confirms that. The site shows the name shows up in United States, UK, France, Denmark, Germany, Norway, Poland, and South Africa. I clicked on Poland, and here is the search results: http://www.locatemyname.com/usa/Sanetra. It shows what they can account for with records and what they estimate the surname is. There's a highlighted map, and statistics given world wide on the name. They also give common first names that go with the surname, and blogs about the surname. My surname of Cabitto is even more rare, and we know all the Cabittos in the United States. Looking at the numbers, I think it's counting adults ages 18 and older. I was surprised and happy to see that my blog you're reading right now is listed on the Sanetra surname!