I assume you mean you need the same resolution. Let's say your encoder is 20 micron per division, 5 micron in quadrature (I'm making this up, do you know the resolution?). The z feed is 5 revolutions per inch, or 25400 microns/5 rev = 5080 microns per rev. Looks bad for the home team. You need an encoder count every 20 microns, so CPR= 5080/20 = 254 line encoder to get exactly the same resolution. If it was a 1 micron scale, you would need a 1270 line encoder.
You can get 254 and 1270 line encoders from BEI http://www.beiied.com/incremental_encoders.html
That's not a standard resolution so it might go for over $500.
I wonder if you can change the resolution on the control? Tons of encoders are available on Ebay for less than $50.