I always wanted to get a cheap set and practise on some locks - where's the best place to find old locks to practise on? I don't want to destroy my front door!
Masterlock #3 is the defacto starting lock to learn how to pick - it's easy, and only has 3 pins, no security pins, etc. They're also very cheap and everywhere, you might even have one already you forgot about.
It's important to get an easy lock to learn on. It'll allow you to learn the principles without a ton of frustration.
For tools, it's difficult to beat Peterson on quality and price.
Picking locks is honestly a great brain exercise. I have a collection of locks, all locked together in a giant ball of locks, and no keys. They sit on my desk, and I pick them when trying to take a break once in a while. It requires a lot of focus, and a mental map of what is going on inside the lock. Pretty soothing actually.
Lots of people swear by Facebook Marketplace but I just hate giving over even more info to FB.
OfferUp can be good, very hit or miss, and Craigslist can be good too - even more hit or miss. I had a CL search running for over 6 months and finally got a worthwhile hit on some local locks yesterday, which was nice.
If you know some property managers, handymen, or property owners, lots of times you can get old locks very cheap or free just by asking.