Where can I find beaters for the KHM3WH hand mixer?

You want part number KHM2B. It's supposed to work with all KitchenAid hand mixers post 1997. Searching for "KitchenAid KHM2B" on google turns up lots of results, including the official kitchenaid store:

http://www.kitchenaid.com/catalog/product.jsp?src=Hand+Mixer+Accessories&cat=223&prod=453

Shipping tends to be expensive. The best price I found was $17.90 including shipping (via usps) from goodmans.net:

http://www.goodmans.net/item.asp?n=KA%2DKHM2B

Note that goodman's has mixed reviews on resellerratings:

http://www.resellerratings.com/store/Goodman_s

Bryce Allen
December 2007