Are you looking for the tiny bulbs that form a circle around the outside of the pinball bonus box where the bare bulbs are visible to the player?
If so, they're called Tivoli bulbs (possibly Tivoli TL2437, but most places I've seen just call them Tivoli), and while they're difficult to find they are still out there.
If you're interested in replacing them with incandescent bulbs (which is how the S+ Pinball machine was outfitted from the factory and looks better in my opinion than LED), try contacting NLG member "brokenticker". He posted years ago that he had a bunch of the bulbs (
link here) and to the best of my knowledge he does indeed still have some as recently as about a month ago.
If you're hell-bent on changing them to LEDs, Spin, Inc. has them (
here), and Patriot Gaming has them in assorted color options (
here).
No endorsement of either of those companies is implied, although I have personally ordered other items from Spin, Inc. in the past and did not have any complaints.