A norton is a nice bike, but as far parts go it depends on how old of bike you are looking at. I have a 20 year old harley and it can be tough to find parts for it sometimes - I ride with a guy who has a late 70's BSA he is in a constant hunt for parts. If you do go with an older bike I recommend researching what is the most common problem with the mechanics of the bike and keep an eye on ebay for those spare parts or check out swap meets. Start collecting extra parts for cheap when you can, so that when something goes wrong you are not spending weeks searching out obscure parts and paying through the nose for them. When ever possible pick up a spare carborator (or two), gaskets, electronics, etc.. Also, there is quite a community of riders around cafe style bikes, get to know them as they are indispensable when trying to locate parts - I here the Black Dice bar on Dundas west is a hot spot for cafe racers, so maybe start drinking there.
Alot of people ask me why I bother riding a 20 year old bike (my other bike is 30 years old) and for me the answer is simple - most of these old bikes you can fix yourself with minimal tools. If you are willing to read the manual and get your hands dirty then you can do the maintenance yourself and fix many of the mechanical problems that arise. By learning to do this stuff yourself you not only save money, but you develop a different relationship with your bike - there is nothing like the satisfaction of taking your bike for a spin after spending a day diagnosing and solving an electrical problem.
If you do buy an older bike be careful of what you are getting - when a bike is +20 years old it is likely that it has had many owners, and you never know what "modifications" have been made to it. When you go to look at a bike bring someone who knows about bikes with you, or make sure you take it to a mechanic you can trust to have it looked over before purchasing. As far as mechanics go, I know Rosey Toes is highly recommended ( I have never dealt with them).
If you are not into working on a bike, then I suggest buying newer bike that's dressed up like a retro street racer - I hear Triumph and a few others are making these now.
Good luck, hope to see you out on the road.
