Thank you both for your answers and help. What I have decided to do is to order a new mitre guage bar for my table saw, then drill and tap it to fit the tenoning jig. The saw came from Charnwoods and they seem pretty helpful so I have high hopes of them being able to supply me with one. If not I have some Aluminium the right thickness which I can cut to width on my bandsaw and just touch up with a file. I must admit that I like the little washer on the end that fits in the T slot, I could probably make one of them too if I need to.
I notice by my name at the side it sais I have not thanked anyone, but I am sure I have. - is there a special way of doing this?