They're larger than a quarter but these are the original cockpits lights on my 97 2320.
https://www.perko.com/catalog/lighting_fixtures/87/reduced_glare_design_cockpit_light/
$75 SHIPPED
Brand New But Not In Packaging
Includes Light w/ (3) Batteries, Whistle & Daytime Flag
Replaces USCG Flare Requirements
C-1003 eVDSD SOS Electronic Distress Light for Boats
I originally posted about these about a year ago:
https://www.classicparker.com/threads/perko-transom-bronze-thru-hull-scuppers.21128/
And was just able to find a source for these where I didn't need to buy 10. Perfect to replace the plastic transom thru hulls on our Parkers.
Just getting an...
Most of the locking caps I've seen come as a whole assembly.
You can try something like this that prevents siphoning from the fill:
http://www.vetusmarine.com/store/p/387-Fuel-Theft-Security-Device.aspx