I have the same rig. (the later HTX-10 has a better receiver, but lacks
CW) I believe the mike UNIT is limited to Radio Shack, but using the
schematic you should be able to set up a remote control system like I
did- boom mike clipped to headphones, footswich for tx/rx switching and
pushbuttons for up/down use.

Good luck, and enjoy it- it's not a bad rig for the price! (and just
wait for the sunspot count to rise again...hubba hubba!!)

"Peace is that brief moment in history when everybody stands around
reloading."
Rev. Skip Heitzig