Lawson,
It came from Quest Outfitters, but that was five years ago.
The stuff they have now is OK, but pretty much standard for the best I've found here in the US, Suter testing at around 15 kPa when the water starts to penetrate. This subject is discussed by Roger in the most recent MYOG thread on silnylon.
Since I make tents only as a hobby for self and friends, I have enough of the older stuff for a project or two more, but that is all.
I started getting frustrated about silnylon in 2005 when I was almost finished with a very difficult tent – a real labor of love (or obsession, depending how you look at it). Decided to squeeze a little water through the silnylon, and discovered that it required very little pressure to do so. So ordered the stuff from Quest, and got some from Warmlite also, both of which required a lot more squeeze before water drops came through. Not very scientific, and I got ragged on a bit on this site about that, but Suter testing later showed that the Quest was indeed much more water resistant than the silnylon I started with (That was from OWF, and also had the "wet look" Roger talks about, but so did many if not all the silnylons available then.)
I did have very good luck using Thru-Hiker's black silnylon purchased last year for a floor, and posted about it the end of last August, but Suter testing showed that it was not in the same league with the older stuff from Quest. Although it rained constantly for 10 days, the T-H floor was exposed to more sheltered sites, and not pitched on puddles or anything like that.
So I will use up the older stuff, and hope that material with better coatings becomes available to MYOGers here in the US, because I really enjoy dreaming up tents and making them and flies for myself and close friends.
Lately, I've been looking just about everywhere, but with no success. So I agree with Roger, if I understand him correctly, that the quality of material that was once available here is no longer. As with many other products we seek for backpackinglight, there are a lot of nice sounding claims out there, but living up to those claims is another matter entirely.
So I sincerely wish you good fortune should you quest for good materials.