While looking for some details on an Armenian festival mentioned in someone's post, I stumbled upon the following site. WOW! Using that as a starting point, one could probably find 50 times as many ethnic festivals as currently being discussed.
Unfortunately, it seems to lack GREEK. But it might prove invaluable in tracking down Russian or Polish festivals.
In fact, it has already served me well on finding the HAWAIIAN one.
Wish I had found it like 4 years ago.