Issues in developing on OSK5912 (OMAP Processor)
I know very little about Linux (not used it for years) but since there are no other answers (yet) I will post my thoughts:

Are you sure the PRO 5.0 version of Montavista will not support your board? I had a look on their website and on the board support page, if you select platform as PRO the OSK5912 is listed there (it says 3.1 but the filter is for 5.0, so maybe it covers previous releases), suggesting it may be supported. Here is the link:

Board support page with PRO filter selected

I didn't check TI as I'm not sure exactly what you would be looking for, but often vendors will keep archives of old tools, so it's worth having a good look on their site for anything you need (or maybe send them a quick mail telling them what you are trying to do). Google is good at finding old software too, which may not be necessarily on the original vendors site (maybe an archive or torrent set up by someone else)