I re-found a site I found back when I had my calipers powder coated:
Pro-Bolt Stainless Steel Bleed Nipples

They sell a variety of stainless bleed screws for calipers!! I know it looks like they cater to motorcycles, but I did contact them way back when and they said they should be able to assist and getting stainless bleed screws for cars (if they don't already have them).

I did not end up using them because I did not have the time to mess with matching mine up (though I would love all my cars to have stainless bleed screws).

Since I found this link again, thought I'd pass it on to everyone here (as I don't know if I've ever seen stainless bleed screws before, they are always ZINC coated).

 

A lot of manufacturers switched over to stainless in the past few years so a lot of the replacement screws are stainless even though they may not mention it in the description. The price isn't a guarantee you'll get stainless, but they are usually priced around 4X that of their iron counterparts.