Well damn, so they're no longer available?
Some still are. Check Amazon.
Problem with the Targus Stowaway fold-ups was that they were device specific. AFAIK they only did them for the Palm, Handspring, and Clie.
I had one for my Sony Clie until that died. I ended up giving my keyboard to a friend who had one that still worked.
I really miss my Clie. It was a simple and reliable device that didn't try to do too much. But what it did do, it did brilliantly. I wrote the entire first draft of a book on that little bugger. Too bad Sony scrapped it's PDAs and went completely over to smartphones.