Sooo.. you want one of every release, every design ever made?
Interesting goal.
I have been collecting for 10 years and have purposely not completed my collection

That Wiki page is a good start to see what all is out there. Then there's ebay. I sell some on my site.
I'd think a funner way to collect would be when you find something new, buy it!
There are a LOT of special edition Gen1 and Gen2.
There are not nearly as many special/limited edition of these new big Tamagotchis.
Aww crud.. I was going to show you a page of rares but AOL shut those pages down

I have a lot of designs pictured on my site but hardly full collections as I am not interested in completing what I have. My Gen1&2 is pretty thorough but not new stuff.
http://www.tamenagerie.com/tamagotchi.html