Not sure where to buy from, as I usually buy my guns second hand off of forums etc.
As for which is better: I've had a Tokyo Marui P226, and I currently have a KJW P226. I've used a WE quite a bit too. I would go for the KJ Works if I were you. The reason is that the only problem I've found with KJ works guns are the magazines (crappy quality and always leak even when looked after properly.), but the KJ works P226 takes Marui magazines anyway so you can use those and they'll require a lot less work than a KJ mag to maintain for about the same price. WE replacement parts seem more plentiful, however I think it's mainly because they break more often, that seems the trend with my friends' guns.
Basically my choice would be the KJ Works personally.