I wish I'd known you needed a 36" -I listed on on Ebay, that so far is going for $5 :/ A Weaver Smart Cinch.
I got mine off ebay; I can look back to find the seller who sold it (they had an ebay store, I think) 36" was the largest I could find at TSC I like my sidepull, I admit. I got it off ebay, as well as two rope halters sold/made by the same person. I'm very pleased with them all. We were discussing the merits of training Trixie in a sidepull, and not bothering with a bit. Unless we show, it really isnt' necessary, unless you want to make all the horse folk with no-how happy.
Meader Draft Supply is a good one, but they have mostly driving stuff. Other than that...right now all BlackJack's tack is off ebay, except his SLT bridle.