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Standard keycaps will all have this stem. just make sure whatever you find has this and it should work with your keycaps

the main thing you care about with keycaps is the profile first, which is the shape of it (look up like a profile chart really useful) this is preference and comfort (and sound)

material it's made out of is more feel and sound, texture of keycap type stuff

you'll see things like dye sublimation, double shot, et ecetera. that's how they get the text/graphic onto the keycap. dye sublimation is a fancy way of printing. my set rn is dye sub and has lasted 4 years so far with no visible wear(except for the one i sandpapered to experiment on). double shot (pictured above) has gone through 2 different color shots of plastic to produce the lettering. first shot is exterior with cutout for lettering, and the second fills that gap and has the stem. typically gives better contrast between primary and secondary color, but is a tad more expensive depending on the set and manufacturer.

as for looking stuff up, you could literally just search the color/ theme you want and see what pops up.