Not much point in trying to sell patterns if your customer base can't find material.
Perhaps some do, or have ads. The Vogue website has a locater for stores that sell their patterns (which are logically also fabric stores) but for my area, all that come up are Joann’s and G Street.
I haven’t been to one of the large Joann’s ‘superstores’, and it could be they have a better selection. I just don’t find much quality stuff in natural fiber.
Color on computer monitors is getting better, and if you know fabric you can probably do well with online shopping. But it’s not the same.