I'd avoid any generic Chinese eBay offerings - they may be fine for bodywork or low stress applications but you wouldn't want to rely on them in safety critical areas like yokes or engine casings.
You need to check that the tensile strength of your replacements is at least on a par with the originals. I don't know what the rating of the standard bolts is as there were no markings on the heads of mine but, for reference, Probolt say their caliper bolts are rated at 570MPa.
I use these people
https://www.kayfast.co.uk who also have an eBay store
http://www.ebaystores.co.uk/Kays-Fasteners.
They're British, cheap, you can buy individual screws and postage is very reasonable. Highly recommended.
The zinc plated screws in the picture are probably closest to the standard finish and, with a high tensile strength of 1200+ Mpa, are well up to the job. The A2 stainless screws would also be fine - while it doesn't show the tensile strength on the website, they are stamped A2-70 and the 70 indicates 700MPa.
I fitted the black high tensile bolts in my forks. They aren't coated or stainless but, with moly grease on the threads and heads dipped in ACF50, I've not had any corrosion problems.
Many bolts have a code stamped on the head telling you the tensile strength - this chart will help you decipher them.
