I don't know where you'd get the parts to rebuild one, short of having them custom-manufactured. Even the correct microswitches are hard to find, which have a 13.5mm lever (shorter than most microswitch levers). The original ones were Matsushita AH76515 or AH76525, with the newer equivalent being Matsushita/Panasonic AM51661A5 or AM51661C5.
Aside from the microswitches, there are a few things that tend to go bad on an SNK LS-30 joystick. There is a metal post which fits through a metal slot and both of those wear down. The post gets flattened on the sides and the slot gets wallowed out. This gives it extra play when you first twist the joystick, or especially when you first twist in the opposite direction that you've been twisting in. There's no way to fix that short of finding or making replacement parts, or doing some fancy welding and reshaping.
Another thing is, the rotary switch gets harder to turn and the individual clicks become less distinct; I assume it gets gunked up and/or worn internally. I don't know of any way to take the switch apart without breaking it.
The internal nylon bushings wear too, and those aren't off-the-shelf parts either.
About a dozen years ago there was a website that sold NOS LS-30s for something like $15 each, and did so for quite a long time. People took it for granted that they would always be cheap, and many, if not most of them, ended up in MAME cabinets (unfortunately). Then, overnight, he jacked the price up to something like $80 each when he started running low on them, and they've been expensive ever since, no matter where you get them.