You can buy Gephardt's chili powder at Texmex.net:
There's a link to an order form at the bottom of the page. I called them on the phone for some chili advice and, I think, ended up ordering over the phone. The guy was very helpful.
To make the shipping charge as cost-effective as possible, I ordered the big, 5lb. size. That was at least two years ago and I still haven't used it up
You'll notice that they have other texmex products, too. At the same time I ordered the Gebhardt's, I also ordered their cumin, liquid smoke and their hamburger seasoning; you mix it with the raw hamburger before grilling. It's delicious.
And... the guy I spoke to on the phone threw in a few free dried ancho chili pods, for free!