Unfortunately, official Dell stock ROMS cannot be "dismantled". You can extract the .img file. But it would take extreme amount of work to reverse engineer the .img file and extract the .nb0. Also you still need to write a .crc file for that nb0.
With that said, best things you can do right now:
Complete a hard reset on the Axim (Power+reset hole). If it can Activesync, rerun the Dell installer (
Drivers and Downloads)
In your question, you said "...Dell Axim
WM50 Rev: A12...", I think you meant WM5?
Lastly, of course, if you Axim is still in warranty, just ask for a replacement/refund.