Try a search for "Buñol" on the internet. You'll most likely end up
HERE .
The throwing begins the last Wednesday in August at 10:00 a.m. Don't dress like a foreigner, or you'll be taking more than your fair share of "hits". Get to the Plaza del Pueblo early...and expect at least 30,000 other tomato-throwers to join you.
As for lodging, you're on your own.