Buying pizza dough on the UES
I'd just work up the courage and walk into a good pizza place and ask for one. Many places will sell you one for $2 to $3. Bring a plastic bag or two with you just in case they don't have anything to put the dough in besides a cardboard pizza box. Agata & Valentina makes fresh pizza in their store daily ... I'd definitely ask them. They're probably your best bet.
Agata & Valentina
1505 First Avenue At 79th
Diagonally across the street from A and V is a pizzaria called Italian Village. I would go buy a dough from them (while you're there, have a slice w/sauteed onions or one of their meatball slices). Just remember to leave the dough out on your itchen counter for a while to "warm up" a bit.