Here is a pretty good source for shellac although they don't always
have all the different grades in stock.  They are very knowledgeable
about what they sell as well.  I hope this outfit can help you out.
I have always thought that the more you use shellac, the more you
will like it.  

  http://www.shellac.net/ShellacPricing.html
  http://www.woodfinishsupply.com/ShellacPricing800.html

Good luck now,
Earl Hennagir