I purchased the Airfix 1/24 Sea Harrier from a shop here in New Zealand, when I got it home i found the canopy was broken. I went back to the shop and they took my details, and 3 weeks later a package arrived in the mail with a replacement clear sprue from the importers. I think it took so long beciase they had to get the parts from Airfix, but it didn't cost me a cent. You should try it, after all you've paid for an undamaged kit, and if the one you have purchased is damaged it's up to the shop to sort it out.
Airfix seem pretty good about that sort of thing, at least the importers here in NZ had no problems providing replacements.