Yes, I know, its not an HP.
I also know that people who loves HP models calls "Dark Side" to Texas Instruments.
Well, I readed about a wonderfull TI model in the 65-Notes Vol-3-NÂș-2 page 2.
Its a very very very unusual model.
I think is so rare that you can not find this model in www.datamath.org
Perhaps is more difficult to find than the TI-88 or HP XPander
... but...
here you are:
http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=3114951416&category=9167