You could try calling Stabilized Marine in Florida and see f they have any laying around from take-outs, though I'd guess the plate is part and parcel to the switch and oil light assembly. Then there's the various surplus stores. Me, I'd go the trophy store engraver route; take the old one with you and they may come darn close, in any number of materials. Wait I take that back, as I just spent 1000% more time answering you than I would spend on the problem itself if I had it.
"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"