Quoted from docquest:Cosmos lists them on their playfield parts lists as C-387-6a. You can get a repro rollover that is C-587-6 which appears to be the same.
Swinks and Scott Denissi both have them listed at shapeways. Not sure if they are identical or not. In addition to white you can get them in a bunch of other different colors.
https://www.shapeways.com/product/X9SK45SSM/bally-pinball-rollover-button-c-587-6-ss-em
https://www.shapeways.com/product/EXC4B3BCA/bally-rolover-button
Quoted from EMsInKC:Rat, be careful with those mini rollover buttons. They have a a tendency to stick, and they are easy to break. They are NLA from PBR. I'm sure you can get them from someone on here but they are problematical. I had them on Odds and Evens and they were not a lot of fun to deal with.
If the C-587-6 does not work and there is a slight difference, happy to tweak the design to suit what you need and make it available for you