Radio Knob for 1984 Delco GM

Good evening,
Last time I got my car cleaned by the car wash they lost me a knob ! Hence I'm looking for a very specific part on my OEM radio for my 1984 vette : The CrO2 knob. I saw a few used radio with it on Ebay but listed at +/- 200 or 300 canadian$ + shipping. I was wondering if you had any suggestion where I could find this specific part ( a specific shop you might know, somebody here that might have the part...

Thank you in advance

and would be interested to sell it....