Hi, The Benellimotobiclubgb has all the uk spares for your bike so worth calling them ( [email protected] )
i think I may have a seat will check my garage and let you know. There were some spares on EBay for a cross recently aswell.
i always find looking at eBay Italy good and the stuff always comes through ok!
i have a slightly later version of your bike it's the 125 enduro