On Thu, 09 Nov 2017 15:19:50 -0800, Joerg
wrote:

Missing a couple of screws for mounting adapters and calipers. The frame
of the bike is aluminum.

Do these have to be from some sort of space-age special material? The
ones that came with the adapters (unfortunately only one pair each) are
magnetic, so it's steel.

Most of my M6 screws are Cadmium plated steel like they are used on
aircraft. Will that do?

I guess brass isn't sturdy enough. Anything else is locally unobtanium
in metric size.

Sure, I use stainless screws on my bikes. Mostly because there is a
shop nearby that stocks both metric and imperial sizes from ~1mm up to
about 1/2" in various lengths.

Common stainless screws are generally not as strong as common steel so
perhaps steel might be a better choice for brake attachment. I think
I'd just use the steel bolts with a bit of anti-seize which would
insulate them from the aluminum and prevent galvanic corrosion (which
I think that you are worrying about).
--
Cheers,

John B.