Cummins also has a good supply of G41 rootstock... and probably others as well. Their site shows it as being sold out, but that link is evidently left over from last year.

Cummins website is not updated with rootstock. I had ordered a few G.890 last fall but just e-mailed me that it won't be available. They said they do have G.11, G.16, G.41, G.30, G.210, G.202, and G.935.