Hello John,
If 27 TPI thread guide are not available for the Unimat SL I can think of at least two ways to make a thread master to fit the SL.
(1) If you have access to a thread cutting lathe you can make an exact copy that will mount right on your SL. This would be my preference.
(2) You can buy a 1/8-27 straight pipe nipple from a hardware store and use it as a master. These can be purchased in fairly long lengths and they are often used in lamps. Of course, you will still need to make a follower to mesh with the master. A 1/8¡±-27 pipe fitting could be pressed into service for this.
OldToolmaker