If you have a modern SUZOHAPP door, great! You can go to their web site and order parts. But you’re better off going through a reseller, as Happ’s markup is substantial. Third-party sellers seem to have the same parts for less.
Happ probably still has some parts for their older WG/Coin Controls coin doors, too, but it looks like fewer and fewer.
For Coinco, good luck. You may need a donor. I’ve had some luck with Arcade Boneyard. I have seen some NOS parts for sale from Pinball Resource in the past on their Specials page.
I’ve found some Entropy stuff from Pinball Life in the past, notably reject buttons.