For $130, you can turn any Pilot or PalmPilot model into a Palm III, complete with all features except backlighting.
Free updates for each Palm OS version are available on this book’s CD-ROM (and from the 3Com web site). They’re well worth installing, if you don’t already have them, for reasons of stability and memory management.
If a Palm program is causing problems for your Palm IIIx, Palm V, it’s probably because of an incompatibility with the new Dragonball EZ processor (or the Palm OS 3.1 that accommodates it). Check the software author’s web site for an updated version.