Hello Mike,
The warning lamps used to show up on eBay and other online sites frequently. I haven't seen any in quite some time. The problem with these lamps was the short two-year utilization on the '72-73 models. The hated seat belt interlock system was introduced in '74, replacing the '72-3 warning lamp/buzzer system. None of this was the manufacturers doing; these were all government-mandated systems. Yep, the same ones that are always busy spending your money and protecting us from ourselves!
The lamp used in the Mustang, D3ZZ-10B925-A, replaced D2ZZ-10B925-B; both had a black trim bezel and were also used in the Cougar.
The lamp used in the full-size Ford, Gran Torino, Pinto, and Maverick, had a chrome bezel and was a little more plentiful since Ford used it in more vehicle lines. The part # for it is D2AZ-10B925-A. I found one source that shows a small inventory of those. I haven't had any business dealings with them, but you could contact them and see how proud they may be of them.
https://www.rearcounter.com/D2AZ-10B925-A-parts2216210.html
You could also check with Mike @ Motor City Mustangs or Don @ Ohio Mustang Supply (OMS). They are both members/vendors here and have parts cars.
If you wanted to eliminate the light and not want the appearance of a cover in that location, you could replace the right-side finish panel with the version used in '71-72 Mustang built before 12/1/71. Since your Mustang is a vert, it has the same trim panel that is part of the Mach 1 Sport interior group. The part number for that panel is D1ZZ-6504338-B and is available as a reproduction.
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