If anyone else ran into this, I ordered an Attwood. It appears to be an exact replacement for the original. I didn’t even need to install the new base; the cover fit on exactly. Word of caution, make sure you tighten the cover hard until you feel a click. It will not be secure otherwise.

attwood Deck Mount All-Round Light
https://www.amazon.com/dp/B002IV89LQ..._YS9CDbETVP0M0