Even if you found somebody that would sell you a card -- you'd still need
HP to come out and complete the install.  The CPU most likely contains the
HPSUSAN number and HP USERLIMIT.  That information must be copied from your
old card (you do have a record of that information correct?) and installed
into your new machine using SS_CONFIG.   Only HP has SS_CONFIG,  it is a
proprietary tool.   There are several ex-used equipment resellers sitting
in the U.S. prison system because they had illegally obtained a copy of
SS_CONFIG and were using it.    That also would explain why you haven't had
a lot of interest from the resellers.

There are third party maintenance companies --- contact one of them and see
if they can help.  If you do, verify that they are licensed to use
SS_CONFIG and the diagnostic tools.