I can't help much either, but I did find some polkas in a recent search for Irish fiddle tunes. (Polkas are Czech/Polish originally, of course, but the Irish seem to have adopted them.)
This is in pdf format, and you need to go all the way down to the end (pages 24/25).
http://www.ceolas.org/pub/tunes/tun...essionTunes.pdf
You could study these and try and identify special characteristics. E.g., they're all in 2/4 time, quite uptempo, and mix 8th notes with 16ths. Four of them are modal (dorian or mixolydian), but that may just be an Irish thing; the other three are major key.

I presume you've done the usual google trawl?
http://www.polkacatalog.com/store.asp
http://www.internationalpolka.com/
http://en.wikipedia.org/wiki/Polka
http://www.answers.com/topic/polka

And yeah... how come you're asking this on a metal site??
(And how come I'm answering it???? )