Hi Terry
Give these guys a ring, Patriot Chuck Thread Adaptors and Excerts (oliverswoodturning.co.uk) they may be able to supply or offer advice. I used to own a Tyme Cub many years ago and from memory the thread was 20 x 2mm. I still have the info saved on a hard drive somewhere and I bought a suitable tap to make up my own faceplates, actually I still have that so could check the size easily.
EDIT
Just looked and the tap I have is an M20 x 2.0 (second cut) so the size is as I said above.