Where can I buy the Pokemon episode videos from Season One?

Question

I'm talking about the Pokemon videos that had three episodes on every video and sometimes included the Poke Rap at the end. I believe that they were done by Viz Video, or something like that. I have been fortunate enough to find some at some local thrift stores, but I want to collect them all.

Is there a place where I can buy them, like a website or a store that isn't a thrift store? Thanks for your help!