Hmm....I don't know if Beretta has the parts you want anymore or not...
I just looked online and saw that their Inox models have black accessories on them:
but when they first came out, they were ALL silver:
Hopefully they haven't "streamlined production costs" and only make black accessories now leaving you high and dry if you have one of the older models of the inox pistols....but it would not surprise me if they did. it's cheaper to make a million of the same part in black, than it is to make 500,000 in black and 500,000 in silver/stainless finish
IF Beretta can't help you, maybe you can find a GOOD gunsmith who can take your stock parts and machine them all down a few thousandths, then nickel plate them for you? I have a 1911 that started out as a stainless model, but it's been nickel and gold plated, yet all the parts still fit together, so the guy who did the work knew how much to remove before the plating process and still have the parts fit together.