This sucks. Mark is a strong advocate for surround sound music. His mixes are excellent. One way to support him would be to buy his product through his website. I'll look for the link.
It might be prudent to reach out via the "contact" page first. I don't know, but I suspect AIX is more or less a one-man operation, which means that while Mark could have an external warehouse somewhere, it's not unlikely that he kept all remaining stock at his house.
I would encourage anyone who does not have this disc to either buy it directly, if possible, or seek it out on ebay. The mixes / sonics are excellent. Also, I used the test tones on this disc to get true balances for my 7 main floor speakers