I had this issue when I had to leave my stock behind when I moved and was really lucky in finding a broken one (an L96 that is) in the classifieds section of Zero In after posting a 'wanted' thread there. Took a month of bumping though. I went to a lot of retailers too before that but turned up nothing. Even tried some US sites where they have a lot of broken stock and they said the L96 stuff goes really quickly when it's on sale in their 'boneyards'.
If it's fixable, try products from Plastic Paddding - the Gelcoat Filler I have is basically liquid plastic and is super hard wearing but also sand-able plus it bonds to what you stick it on. May be worth a go.