Where/how do you get them? I saw that you could buy an unlimited use kit with diamonds, but how do you get the single-use kits?

outside of the newbie pack, you pretty much can't (might be some for one of the Advent Calendar days, but the ones last year are painfully Untradeable.) Used to be you could get them from a wheel during Fest time as a prize, but that wheel was discontinued. Same for Genetic Scanners.

People do offer free testing services, though.

(Saving up the Diamonds(/gold to buy diamonds) to get the unlimited ones is really worth it, though, gotta say)

Ahh. Thanks! Guess I'll need to save up for the diamond one. :)