I just received two rolls of medium/heavy weight lead double-primed canvas that I ordered for some larger paintings. I ordered one roll of gray and one of white (photos below). I've noticed that medium and heavier weight linen works well for larger paintings because the lighter/finer linen tends to pucker and warp.
This beautiful canvas is from A.E. Art Canvas Priming in the Bronx, N.Y. - I've written about this company before, but I want to give them another shout out because Mr. Angel De La Cruz is a great craftsman. He does completely custom orders so whatever you want, he makes. This is difficult to find nowadays and it's especially difficult to find lead primed linen. Also, before I ordered, he graciously sent me samples of linen (for free) to see which one I preferred. You can reach Angel via email: email@example.com and their address is:
A E Art Canvas Priming
605 East 132nd Street
Bronx NY 10454
Here are some images of the heavier weight double-primed lead canvas - linen #77