Hi Terry -- I had the same issue a while back, and Ed Cave was kind enough to put me in touch with his restorer, who in turn led me to a fellow in Michigan that replates plastic.
He did a terrific job on my two sets of Frigiking A/C vents for reasonable price.
If you'd like the particulars e-mail me off-line and I'll get that contact info for you.
Tom in Boise
'71 280SL 4-spd, signal red w/lt. tan interior, restored/enhanced