Someone else will have to advise you whether that one is for still sale.
Buffers are relatively simple circuits that have been around for a while.
I have guitars with both CAE CB-1 and Wald buffers. They sound identical to me:
CAE CB-1: http://www.caesound.net/cb1guitarpreampbuffer.aspx
Here's another company, CAL, that makes a buffer called Redeemer (I've not personally tried this one):
FYI re: installation:
https://www.premierguitar.com/articles/ ... rat?page=2