http://www.southcoaststainless.com/
It might be difficult to find the right polished stainless hardware at the local hardware store. I have used these folks in the past and they should have what you need. Just make sure to order some matching nuts to chase the threads after you cut one down to the correct size. You DON'T want to cross-thread the window frame holes. Install the nut on the fastener, cut the fastener to length, then remove the nut (thereby cleaning up the threads).
Good luck,
-Dean