If your local cake decorating supply store doesn't have it, try a health food store. You can get a lot of great stuff for cakes at health food stores.
Michele
OK, I know that some will have a problem with this, but here goes--you can buy 100% pure cocoa butter in a stick at Walgreens (and probably many other drug stores) for .99/ounce (a great price). It comes in yellow tubes by Cococare.
Yes, yes, I know that it isn't sold as "food grade" (but my way of thinking is that if it's 100% pure cocoa butter with no additives, I don't see how it could present a problem), etc., BUT....
I found out about this while taking a class with Roland Mesnier, the White House Executive Pastry Chef (for over 25 years) and I figure that if the Secret Service allows him to use this on PRESIDENTIAL & WORLD LEADER desserts, etc., then it's good enough for me. 
He made us some wonderful chocolates having added some of it to increase the fluidity of the chocolate and I'm still here (and quite healthy, thank you) a full week later. Last I checked, Jimmy Carter, Gerald Ford, George H. Bush, Bill Clinton, and Dubbya' are still roaming around, too.
So, since this is something that you would usually need very little of, I think these little tubes are super cheap and convenient--my local cake shops charge between $2 and $4 per ounce for cocoa butter 
Cheers!
Rae
I guess I'm making a trip to Walgreen's today! Thanks for the tip.
Michele
BlakesCakes, I was in Chef Mesnier's class, too! I was the one coughing my head off in the second row! I can still taste those chocolate kisses, mmmmm. I've been out of town the last five days, but I just can't wait to get tempering & dipping! I just loved that class and can confirm that he did, indeed, say you can use the cocoa butter from the drugstore.
I just bought a small bar($1.99) at a cake store this past weekend. I bought it to cook with, but my daughter used it to wash herself in the shower. I won't be using that bar now!
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