They were originally only on wal-mart.com, and have held that domain since 1991. walmart.com was held by "World At Large" until later, looks like 2001-ish. Walmart's branding still used the hyphen (as "Wal-Mart") until 2008.

This is the actual Walmart website in 1996, although there's nothing there to be sold.

https://web.archive.org/web/19961231122316/http://www3.wal-m...