Practice lock cylinder with interchangeable pins and springs. I have one and its good to get experience on a variety of "locks" without much risk. Only pain in the ass is that it's hard to set up to work on and the clamp they sell for it is waaay overpriced. Still, good for any hobbyist.

http://www.learnlockpicking.com/

I cut a padlock in 1/2 with a dremel so I could see the guts.

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I'd be more inclined to drop by the dump, or a used building supplies place. Plus your not going to experience many locks that clean.