Apple has been moving toward fewer field-replaceble service parts, of higher complexity. The thought is this reduces the total cost of parts inventory on hand, since one part on a shelf can be called on to cover multiple possible repairs.
This means that the keyboard today is part of the Keyboard/Trackpad/Battery/TopPlate Assembly, and NOT available separately. Battery service alone is about US$250, and all other repairs that use this part are at least that expensive.
if you has a Much older Mac, substituting a Used part salvaged by a computer 'junkyard' would be the obvious way to go. but yours is still fairly new. I don't see an elegant do-it-yourself solution in this case.