No RCA connector can be 75 ohm. Impedance is a part of cable geometry. The diameter of the center conductor and the distance to the outer shield will determine the impedance. The RCA connector has too wide a center conductor for the distance to the outer shield to come close to 75 ohm.
The "F" type connector and some BNC connectors can be made in 75 ohm. They use very thin center conductors, compared to RCA.
The closest you can get is the design by WBT NextGen where the outer ring is not fully connected. That will then let the cable used determine the impedance. The WBT NextGen male connectors and the Eichman Bullet connectors are designed similarly.
Bottom line, if you want true 75 ohm impedance for digital, you would have to use BNC connectors on both ends of a 75 ohm cable.