Yeah, it seems like Dark-Alex has no interest in following up on 5.00 M33-6, which while long since stale, is now becoming increasingly obsolete. Team Gen have, so far, picked up the slack with 5.03 Gen, 5.50 Gen, and now 5.50 Gen-B. They're basically just aping M33 CFW, but they're getting better at it. They've also successfully dumped and decrypted OFW 6.00, which is a very encouraging (and quick!) development. It seems likely that it'll lead to 6.00 Gen at some point in the relatively near future.
You can simply download either 5.00 M33 or 5.50 Gen-A, and follow the usual upgrade instructions to upgrade to one of those two CFWs. Do patch them up their newest versions, however. 5.00 M33-6 or 5.50 Gen-B2, respectively. I recommend the latter over the former.
Upgrade to OFW 5.03, download the appropriate PSP 1000 ChickHen R2 exploit, and execute the exploit in order to run Hellcat's Recover Flasher 1.60 to upgrade to 5.00 M33, sans a Pandora. Once there, you can continue the upgrade path to 5.50 Gen-A (and then Gen-B2), if you'd like.