Any m6 thread bolt of about 10mm will do, it’s nothing special, the cylinder is held in the backplate and the bolt just stops it from falling out.
I don't think they do come with the green coating these days. I can't say for certain but components I've bought recently look like they are hot dipped in zinc, whatever it is it isn't a great long lasting finish.I want to order them from vw because they cost the same as any other stainless but they come with that green anti corrosion coating which should last for another 20 years.
Btw vw use the same bolt on Bentley V12 engine.
If you are getting the green finish that is great. The last bolts I ordered from Audi came in a flat grey finish.That's strange when I was swapping wishbones and strut bearings on both of my cars, I ordered new bolts from vw not audi around 20 bolts and nuts in total and they all came with that green coating. I could be lucky and It might be just some old stock.