I have a few similar software solutions on my old HandSpring Visor Edge. One is called DOFMaster, which is available through:
http://www.dofmaster.com/
The other, which I use much more often, is called pCAM. This is available through:
http://www.davideubank.com/
The value of pCAM over DOFMaster is that it gives FoV and some other information beyond simple DoF. I also have Vade Mecum 2.1 from Robert E. Wheeler, which is even more complex, though I rarely ever use it due to the complexity.
Anyway, I hope you find a solution with one of these alternatives. Palm software is often the effort of a few individuals, and many just give up after a while, making older software difficult to locate.
Ciao!
Gordon Moat
Dead Link Removed