Hi,
You could buy a cheap unrestricted SV 1999 - 2002 (£1500-£200) (CURVY) model and then buy the restictor kit seperately (£30-£80). Then get your garage to fit it and give you a certificate to prove it has been restricted.
As for buying them restricted, you will hardly come accross one, as people get them at 17 (say) and then get rid of the kits.
Hunt ebay for SV650 and restrictor (used) kit should come up.
If you are looking to get a newer model 2003 - 2006 (Pointy) then it is a bit more expenisve as you will have to buy a restricted ECU (Brain).
Good luck!
Welcome to the forum!