Any down home Salvadoran or Mexican place has orchata. I have had MANY a pupusa and taco washed down with a tall, sweet glass of it. Imagine how many places on Roosevelt Ave. in Queens serve orchata,I can't count that high.
Go to El Paso Taqueria on 103rd and lex. They also have another branch on 97th street. It's Mexcian, but fantastic and cheap too. I have brought many a skeptcal friend there, and they all rave about the horchata.