1) You can burn your own on a 27128 EEPROM with the P800MIDI.OBJ file.

2) You can (as I did) order the eprom programmed and 
   nicely packed with all explanations at 

   http://www.musictechnologiesgroup.com/mtg_eproms.htm
   
   The guy made a backup of a lot of synth (e)proms in the  80s and that's where  I got it.

   It's about 10-15$ in US and 25-30$ in Europe and it's very fast.


I've tried it along with the mod, it's working. Good luck !