Generally speaking, no.
Typically, the contracts that RPGA has with their authors only authorizes the modules to be distributed for official RPGA play. This means that the RPGA can't make modules available for general release once they are "retired" from official play.
Also, most (if not all) RPGA modules contain a copyright notice that also indicates that they may only be distributed for official play. This means, among other things, that it's against RPGA rules for anyone in possession of a copy of an RPGA module to redistribute it to someone else.
That said, there are a few exceptions:
- In the past few years, some RPGA modules (mostly, if not entirely, modules from the "D&D Campaigns", like Mark of Heroes and Xen'drik Expeditions) have been printed in hard-copy form, and distributed to game stores as part of the RPGA's retail program. I'm not positive, but I think that these particular modules can be more freely distributed.
- Many of the newer RPGA contracts have the rights to the module revert to the author once retired from RPGA play; in theory, this means that the author would be free to redistribute the module as they see fit at that point. However, the author would have to remove any RPGA / WotC intellectual property from the module before doing so (which means any reference to proper names, non-OGC rules items, etc.) I'm not sure that many (if any) modules have been redistributed in this way, probably because it'd be a lot of work to take the non-OGC content out.
Also, virtually all RPGA adventures (including, I believe, the Undermountain modules) can be ordered for "home play" -- very few RPGA modules are convention-only. There's nothing preventing you from joining the RPGA, passing the Herald-level test (a very straightforward online test on D&D rules, which allows you to be an "event co-ordinator", and order modules), and then ordering the modules for your home group, though, technically, you still need to run them as "RPGA events" (which means your players will also need to be RPGA members, and you need to report the play of the adventures).