Yes, I think they are 12 x 1.25 thread. I know the Celica from 1973-1977 uses that size (not sure about later ones).
I had the same issue when my gearknob was worn and needed replacing and I didn't want one of those crappy ones that are attached via screws.
I went to Toyota (Castle Hill) and they have the nice TRD all black leather gearknob - same size and shape as the old ball-shaped Celica knobs - approx $40-$50. They also had some fancier shaped ones - approx $120-$150 -all leather also.
However, you need to put a heli-coil into the knob so it can screw onto your gear shaft.
I had no choice but to buy a heli-coil kit for 12 x 1.25 that fits in the new knob and it screws on perfectly.
The kit costs $90 and only does 12 x 1.25 - but it comes with 10 heli-coils. So, if you're interested I have 9 spare h/coils and can do the job in 1 minute. I'll charge you $10 so I can at least get some of my money back - but you'll have a perfectly fitting gearknob that screws on just the way the old one did.
I live at Castle Hill also, so it shouldn't be too hard to get done, if you're interested.
Go and check out Al Palmers site or Toyota and search for TRD gearknob if you want to see what these knobs look like.