By far the best way in the UK is record fairs.
Just buy any issue of Record Collector magazine and all the fairs will be listed. Or you can find a list of their own fairs at www.vip-24.com
As stated before be careful of real boots vs CDR copies.
Bassman is the best source on the net but I do think he over-rates sound quality often.
Then once you've got a few - get a CDr writer and start trading. That's easily the best way to build up a collection.
Good luck and be careful - it can easily become addictive.