If you live within potential road-trip range of Los Angeles or New York (or to a lesser degree, San Francisco) I highly suggest planning an expedition. NY and LA have pretty sizable districts aimed at wholesalers (but largely open to anyone) where you can get damned near anything in the fabric department, including the really fun and exotic stuff. San Francisco has a pretty good selection of fun and exotic, though it's largely via a couple different shops in the bay area and not concentrated in any one place per se. In SF, I'm partial to Discount Fabrics (they have locations in Berkeley and on Haight, but IMO the best is their warehouse in SoMa), or Mendel's (which A-RockLeFrench mentioned and linked). Britex has some interesting and exotic stuff, but is usually premium priced.
Depending on the size of your project and how much you're planning to buy, the money you'd save by going to NY or LA may pay for the gas it takes to get there (my gf and I live in SF, and periodically travel to LA just to hit the fabric district).
Ordering online, the best advice I can give is SWATCHES! Ages ago most places would spot you a few free swatches, but I think most places charge a small fee. Don't let that stop you, pay the fee and get some swatches. Despite some really great photography on some of the sites, fabric is something that (to me) you just need to be able to feel. And given the high cost per yard of fur, spending a few dollars on fur swatches will save you a fortune when it comes time to buy the yardage you'll need for your project. Pro tip: when the swatches arrive, keep them in a bag or envelope marked with where you got them - that way, if months later you come up with another project that may use that or a similar material, you'll know exactly where to go to get it. Good luck!