I recently found the National (Scottish) Waterski Centre at Townhill which is just outside Dunfermline. They've got a website at :
http://www.waterskiscotland.co.uk
They'll give you a short taster session after which you can pay for time on the water behind one of the best wakeboarding boats around!!
Alternatively, if you fancy giving it a shot at Loch Lomond I may be able to help out.
Si