I just received a custom made pre-stretched canvas fron Signature Canvas. My canvas size was not standard so it was custon made. The great thing about this company is they stretched the Claessens 13DP that I use. I love there patented keyless frame which is great for tightening linen as it loosens. The stretcher bars I ordered were 1.5" thick. The adjustments for tightening was no problem. Here is a link to how it works:
http://www.youtube.com/watch?v=1798UfwMQtg
A little pricey but worth the money. Nice folks too!
There web site is: SignatureCanvas.com