This is a very difficult area.
As has been said, many won't want to give their sources to someone who wants to compete with them.
The other issue is the expectation of the wood itself. I suggest you take a good look at exactly what it is that you want. There are 2 ways you can go.
The first is price. If you're looking to get a good deal so you can keep your costs down, then you're looking at buying bulk or lumber. To go this route, you'll need to find many sources, talk to them about availability and dimensions of there stock, and prices. With this method, you get what you get. There will some great wood in your quantity purchase, but there will also be some lesser quality figure.
If figure or quality is what you're after, then you have to buy by the individual piece. Obviously, this is much more expensive. There are sellers that show individual pieces on the internet. They can be hard to get because they get bought out before you may see it, but if you can work out the timing you can get some great wood. Most larger metropolitan areas with have a supplier of exotic woods that you can choose from. There are several here in Dallas. Of course, some time searching the internet and contacting the suppliers you find will get you some good suppliers.
All in all you don't get the cheap prices and the best figured woods. You have to find your comfort level in the middle.