Although the reservoir is different the caps (not sold separately) look similar to the AP clutch reservoir ones on my Roadster. If you can somehow confirm you can buy them here. FWIW Morgan part number for complete early M3W reservoirs is U220019.

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone