The manufacturers website is
here
Parts for it can be got from
BSA Regal who are the importers.Their website also has a dealer list so you may find one fairly close to you.
It's not 'restricted' as such being a 4-stroke, there is no standard higher power version, unlike the 2-strokes from Aprilia,Cagiva,etc. , but it can be tuned.
£700 seems rather cheap to me, how many kilometers has it done, has it been pranged, etc.
I've had an SM for 2 years now and am generally happy with it, though the seat's a pain on long journeys, and headwinds WILL slow you down

. Max indicated speed on mine is about 80mph, the ignition box has a rev limiter at 10,500rpm.
Hope this helps