ok, so when i played (quite a while ago) you used to be able to buy basic genetic scanners, off the broker or something (if i remember correctly). where can i buy them now? i can't seem to find any anywhere!

The ones in the broker were ones being sold by other players, so if other players have none to sell there won't be any in there.
It used to be that Genetic Scanners and Gene Testing Kits were obtained from Festival Wheels as a consolation prize, but the Fest Wheels were retired a few years ago, so now the only sources of one-use ones are newbie kits and untradeable ones from the Advent Calendar.

There are players who have infinite test kits who offer pet gene testing services for free, but other players obviously cannot scan wild pets and enemies for you, unfortunately- really you're just stuck saving up to buy the infinite scanner (which is admittedly absolutely worth saving for)

oh ok! how do i get the infinite scanner?

Diamond shop. It's pricey, so I'd suggest saving up a bunch and buying during a Sale (when they cost 1000dia rather than 1500)

(1k dia tends to cost ~2.1-2.5 mil. gold in the currency exchange, or $10 if you buy for real money from the site)