As Baboon says, loads of spots out there. It all depends where you're staying in Scotland.
The town of Troon is very close to Prestwick Airport and not far from Glasgow (40 min by train) and the spot is very nice (also check out Barassie).
If you're staying in Edinburgh or nearby you can find plenty of info at the Edinburgh and Fife Kitesurfing Club (see Chrisdb post above).
Ask also to the guys on the Flexi Forum: http://community.flexifoil.com/
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Oh and of course don't forget http://www.kitebeaches.com
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The water in summer in not much colder than the Atlantic....so you're set I guess!