On the apache web site there are links for several older releases but it appears that only the last two releases are actually stored on the mirros. I am having issues with the last two releases on Windows 7 as a windows service so am trying to find a 3.5.x release as these were the latest that I have seen working.
This seems to be the most complete archive I could find:
I couldn't find any reference to ActiveMQ 3.5 anywhere (except this thread) – are you sure there ever was a 3.5 release? It seems to jump from 3.2 to 4.0.