I bought my starter shim stock from Kragan auto in California - I think it is Checker elsewhere. It had various thicknesses and was cheap, about 5.99 IIRC.

Here is a link to something like I bought.
http://www.partsamerica.com/ProductDetail....artnumber=02350

Here are some higher quality shim stock
http://www.reliabilitydirect.com/shimprodu...CC-shimkits.htm