If you want thin exotics for inlay or for sign work, try the luthier (guitar maker) suppliers. They will frequently have 'orphan' pieces from guitar back or side sets that they sell cheap. Also headplate blanks are good source for small signs, name plates etc. Two good ones here in California are:
Luthier's Mercantile
http://www.lmii.com/
Allied Lutherie
http://www.alliedlutherie.com/
And if you are into Oregon Black Walnut, then Goby Walnut Products has some great stuff too
http://www.gobywalnut.com/
They are currently having a moving sale.
The best deals from the lutherie suppliers will be had by calling them and asking about these odd pieces of wood they might have.