I have been meaning to have a go at this for some time but I doubt I will ever get around to it, so if you want to have a go here are some ingredients. 1: a bearing mounted flat TV turntable, 305mm diameter, 18mm think (2 x 9mm) and 2: a turntable power kit with motor and gears. The latter still works AFAIK. I used it to make a transverser in my OO modelling days, so the kit also has 2 micro switches and an on/on switch which I added for that project. The turntable holds a 300mm length of track quite nicely (not included). £5 plus £3 P&P to UK mainland address. PM me if interested.
