Yes, eBay.
Plus search your Mustang parts suppliers for fender badges for Gen 1 Mustangs, starting with 1967. Definitely 1968's ran 302's.
If you don't like the style, then maybe take a class or two on 3-D printing. My local library has classes and a printer, too. The cost is less than a decent McDonald's meal, so check your library.
The old Windsor 302 had a 4 in bore and 3 in stroke that was 301.7 cu in.
One liter is about 61 cu in. So a true 5 liter would be about 305 cu in.
Car companies like ‘catchy’ numbers that are not exactly correct.
I liked the idea of listing cubic inch badging before the suits decided to go metric. The sound of 289, 302, 327, 389, 406, 409, 413, 421, 427 just rolled out so easy.
Problem with Cu. In. started when Chevy built real 305 and 307 smog dogs. No one wanted that badge on a car.
The ideal solution would be a new make old style 302 badge or 302 High Performance badge with pins that match the fender locating holes in an S550 5.0 badge. I haven't seen anything like that so far.