The foremost resource of RexxLA is the RexxLA forum, which is open to everyone. Here you are in direct contact with the implementors of most Rexx language processors.
The open source implementations governed by RexxLA all have open, freely accessible mailing lists. Subscriptions for these are handled via http://www.oorexx.org for Open Object Rexx and www.netrexx.org - these point to the respective development reporitories at SourceForge and project Kenai. Also, the Regina project at SourceForge has a set of mailing lists, as does the BSF4ooRexx project.
Another popular resource is the comp.lang.rexx newsgroup, where all implementations are discussed, including Classic Rexx, the original Mainframe version (As is to be expected at usenet, this is an unmoderated discussion group where topics and sentiments vary wildly).
A good set of Rexx (Classic ~, net~, and ooRexx) examples can be found at rosettacode.org.