Several of my friends do or have purchased from Weaver for years with great success. Their prices are good as is the quality of the leather. My only problem with them is that they require a buyer to have either a business license or a tax exempt number. Since I have neither, can't buy there, and have used other sources. Having gone through 2 double shoulders from RJF Leather this week and ordering 4 more, I again want to highly recommend them as a good source.
As quint said, try to buy the very best leather you can reasonably afford. The less expensive, the more problems, the harder it is to work, and the poorer quality WILL show through. Broke my own rule on that last week by ordering a single shoulder from a widely known "factory" because I needed some 4/5oz. fast. Looked pretty good until I started dying and working. Realized right off why I have that quality rule in place.