Same problem here, I’m on 10.8.2 and just upgraded to 6.5.4 in particular to get Retrologue (as I lost Monologue in the Lion upgrade) and neither Retrologue or Padshop is showing anywhere even after a successful install of the trial versions in addition to the 6.5 upgrade.
OK I fixed my problem! For some reason the Macintosh HD/Library/Audio/Plug-Ins/VST3 folder was locked so simply made it Read and Write and the instruments are accessible!
poop that took best part of four hours. No idea why it was in that state!
Cheers, just off to have a play they both look really exciting!