Could you please advise where I can find such telescope; objective
size 40-50mm is OK.

One method is to use a 35 mm camera lens. Not sure what sort of mount you have
with your ToUcam 200mm lenses are available relatively cheaply and probably
more than adequate. I use old Minolta stuff with an adapter from the Minolta
mount to a C-mount and then a C-mount adapter which fits the camera.

jon

jon