You might try
Paragon Reproductions. They list both vented and non-vented chrome filler caps for 1962 Corvettes, at $45 apiece.
PR #: 882
Oil filler cap, push-in type. Vented, chrome finish.
250-300 hp. For Years:1962
#882 isn't pictured online, but here's a photo of the non-vented cap:
