I've always had the fantasy of digging through a pile of random keys for the one that matches, but wasn't sure where to source the keys for given padlocks.
I think the only way to buy keys for them is to buy the locks as well, not sure about abus, but master are the best locks that I have found.
It looks like it's possible to buy random Schlage keys on Ebay for about a dollar or two per, but unfortunately not Abus since I believe they have controlled locksmiths. You can buy Abus 64ti/20 and 64ti/25 from Taylor Security for about three to four dollars each though, which each come with a set of two keys I believe - that's probably as good as you're gonna get.
I came up with a variation on this game when i first started my chastity self locking experiment a year ago. I had a small lock box that i put the device key in. then lock with a generic masterlock on the outside. a couple pounds of random old masterlock keys can be had on ebay for like 10 bucks. got one of the velvet bags they like to ship sex toys in and filled it full of keys. the random old ones that looked similar to my one working one. Then played a daily game where I picked one key without looking, tested it on the lock. then rolled a dice to see if I could remove the key from the bag, increasing my odds of finding the right one next time, or had to add it back. Its a fun game, and a nice way to get into "real" self imposed indeterminate chastity without the fear associated with "emergency release" that a lot of new players, including myself, get. i could always dump the bag out and find my key if i HAD to get the thing off in a hurry, as i painted it black with a sharpie. Ive since moved on to a digital safe and online KH apps like Chaster and Emlalock.