what happened to them ? I had a Q 35 years ago but dont have it anymore. I was a great engine...

They just faded away. Fitting the exhaust pipe or muffler in modern engines is better, Aerow and US engines took over, lots of new manufacturers of dedicated model plane engines in the same size etc etc.

Look at B&B specialities. He still has the whole Quadra line and has excellent service. Very good engines.

Not the Q35. As far as I know it has been replaced with the Q40.
For a while (maybe still?) there was a conversion set on the market.

I have a Q42 sitting in my shop now for maybe 10 years. A very good engine but it's always too heavy or too underpowered to use in what I'm building ( my choice I know ). As a point of comparison I have a Brison 2.4 that weighs 3.5 lbs. all dressed and will spin an 18-10 at 8000 rpms. the Q42 weighs 4.5 lbs. all dressed and will spin the same prop at 7000 rpms, a huge difference. Someday I'll find a plane to put it in.