There were 49,213 Corvettes made in the '77 model year.
There were 41,231 equipped with automatic transmission, leaving 7982 made with M20 wide ratio or M21 close ratio manual transmissions, or approximately 17% were manual equipped cars.
There were 1942 Bright Yellow Corvettes in '77, or about 4% of production.
Extrapolating that would mean roughly 78 Bright Yellow cars would be equipped with manual transmissions. That's the SWAG method (Scientific Wild-Assed Guess).
To go a bit further, of the manual transmission cars built, out of the 7982, 2060 were M21 close-ratio and the balance (5922) were M20 wide-ratio units. So about 26% were M21 and 74% were M20 of the manual equipped cars.
Extrapolating further, that would mean of the roughly 78 Bright Yellow cars with manual transmissions, about 20 were M21 and 58 were M20 cars.
There are no known records that give you the exact number. All you can do is take the known numbers and work the percentages and that should have you in the ball park, but it's no certainty of any real accuracy.
My numbers came from the Corvette Black Book and I worked the numbers from them.