Buying blank sketch covers? 0

[TheCollector2016]

Perhaps I'm looking in all of the wrong places, but where exactly does one procure a completely blank cover for an artist to create a commissioned sketch cover?

And related question: If I commission an artist remotely, and agree to meet them at a convention to pick up the sketch cover, if a CGC witness is present, is that sufficient to have it submitted for the yellow label?

[MOStateSuperman]

You can buy them from comic shops - they're generally solicited as a variant alongside standard covers. I used to buy stacks of them from Midtown. I didn't end up using nearly as many as I purchased, but I used a lot of them for exactly what you're describing. You can usually send a blank to an artist (as long as they agree) and meet them at a show for pickup. As long as CGC (or a facilitator/witness) is at the show and is with you at pickup, it will be eligible for the yellow label. 

[Will_K]

I get blanks on ebay.  At conventions, there are some dealers that will have a box(es) set aside with only blanks.  If a small comics publisher is at a convention, they may also have some blanks.