I really had no idea it is that popular. I worked at a scrapbooking store. We kept only a minimum amount and it sat on the shelves forever. No one ever even asked for it. I go to big crops 4 times a year and rarely ever see anyone use it.
I like thicker vellum sheets - they are great to punch shapes from, like snowflakes for example . they look cool. but it's a challenge to find colored vellum, unless you have a stash from the old days.
DCWV still makes those vellum quote stacks, don't they? they are a bit out of fashion, with the die cutting machines and such
There's a great art supply store here, Flax, that has amazing art papers, handmade papers, all kinds of vellum (colored and patterned), card supplies, etc. And another art supply store has several different weights of vellum.
You can also get great vellums (and other marvelous papers) at specialty paper supply companies like arccrafts.com, papertemptress, and of course here at sb.com!