I bought mine online. Can't remember offhand, but check here for prices
with shipping:

http://www.paragon-products.com/product_p/swepco-201.htm

I used the 203 product, available here:

http://www.cdoc.com/detail.asp?id=19663&str=5010-
1512&name=Gear+and+Differential+Oils

Both products are available here, but a but pricier:

http://www.pelicanparts.com/catalog/shopcart/CARE/POR_CARE_SWEPCO-
detail.htm

You can also try eBay.

- Kevin