The link below will direct you to your nearest ReStore in North America, elsewhere in the world there are apparently other places in which you can buy used building supplies.
http://www.habitat.org/restores
Your mileage may vary, I've found some that try to be essentially a second hand home depot and others that feel like walking into a warehouse sized flea market stall.
I went to one of my local ReStores(the other doesn't have much of anything) and ended up walking out with 13 mixed deadbolts for practice for 10$, the prices seem to be somewhat arbitrarily decided by the cashier and I was originally quoted 5$ however I had to leave for an atm and the cashier when I came back decided on 10$, I still felt this was more than fair because of it going to charity and was somewhat happier paying this surprisingly.
There's a few recognizable locks in the collection, mostly kwikset and the like, one I couldn't figure out however is the one below, anyone have any idea what it is? The design of it seems different that most of the major deadbolts i've seen, was this a common older style dealbolt?
One thing I would like to add however, is the store is a great source of low cost parts and i've heard of and seen instances where perfectly usable locks were ripped apart to get the price of a keyless cylinder, out of respect please don't do this, there are people who could and would put those intact locks to perfectly good use. If you really want a lock that is still in tact buy it as is and let the charity have the money at the very least. Why rip off a charity over a couple dollars when you're already saving plenty.
Any other good sources of locks for beginners or those building their collections? Particularly more advanced locks, I've heard ebay is good however ebay canada seems much less fruitful.