are there any guides to buying LEDs? i'm looking for something like this:
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and don't have the slightest clue where to start, as well as other 'specs' i need to take to take into account
most people buy theirs from chinese eBay sellers.
as to what specs to take into account, that can be an extremely complicated answer, with power requirements, brightness levels, forward voltage drop etc etc.
In practise, most any LED you put in a keyboard that has resistors already soldered will work. The worst-case scenario is usually that it wont be very bright.
Teal LEDs like that are usually either white LEDs that are tinted or a semiconductor that actually emits teal. Both should be in the higher range of voltage drops and won't flow as much current as (say) a red LED. But it's brighter at less current, so it evens out relatively well.
It's beyond the scope of this thread, but if you give us some specifics on what kind of LED you're after and what sort of KB you're putting it into, we can help you out more specifically, but usually it'll just work.