650 x 25c?
 

Anyone know where to get this size tire?

Pretty unlikely; why not go with a 23c instead? Many more manufacturer and price options. Terry offers a 650x28, but it seems like manufacurers would determine full width runs of 650s to be cost prohibitive.

http://www.chucksbikes.com/store/ti020.htm

650x23c there

I'm building an old crappy 650c nishiki tri frame into a beater for NYC. I was planning on lacing 26" mtb rims to some formulas and using narrow MTB tires for better cornering and a little bit cushier ride, but I stumbled upon a 650c wheelset so I'm looking for a little bit wider tire for said wheelset. If it doesnt exist, I'll ride on 23c's without hesitation. Thanks dudes.

Bontrager Race Lites, Race X lites, Race Lite Hardcases etc etc etc.....
http://www.bontrager.com/Road/Wheelworks/Tires/5730.php

rad. thanks.