I don't have any tips on how to make a bow with velvet (haven't done it yet!) but I know when I purchase mine I will get it from http://www.ArtisticRibbon.com
. They have imported Swiss velvet and that is supposed to be top of the line. Their prices are pretty good - but you have to buy a certain quantity to get the wholesale pricing.
I order all my other ribbon from them and have been very happy with their service.