Canopy hinges are Mini Mark 1 external door hinges, bottom apparently if you want to be particularly picky. You can get new sets from MiniSpares and MiniSport for around £30 a set or a pair, I can't recall, but it's not bank-breaking prices. There are other suppliers too - some sell only a set of four hinges but at least one place sells them individually. I was going to replace mine but then changed my mind, and sorry but I can't recall off hand which place offered individual hinges. Given that they're sat on rubber gaskets, I can't think there's any practical issue with using top or bottom, or one of each, but as I say best practice seems to say the bottom. And they're handed of course. Might be worth a chat with Dave Hemsley at BugSpares.
I don't know if this company could help - Gold & Wassall Hinges Ltd of Tamworth. Somebody told me about them today in relation to some old caravan hinges - but I expect they do other hinges as well, and as they are in Tamworth (ie close to Reliant), just maybe they might be worth a try ?