Whats a good reliable source for Sony US18650VTC4?

Thinking about building a small 12S4P pack with them.

Have you considered the new samsung 24R? They seems to be even better than VTC4s (capacity)
http://dampfakkus.de/akkuvergleich.php?akku1=79&akku2=170&akku3=484&akku4=485&akku5=490&akku6=&a=5

Don't know where you live but here is a reliable one
http://www.groetech.de/index.php?main_page=product_info&products_id=111

Several ES builders have bought from this guy when he was "supowerbattery111" on ebay, now they have their own shop:

http://www.batterysupports.com/liion-battery-c-4_5.html?page=2&sort=20a