What size plate for 2 1-gang boxes side by side
Short answer: No

Whoever installed the boxes didn't learn how to do electrical work properly. So consequently, you have two single plates that have been trimmed.

If you were to find a plate like this it would be a custom item and may cost more than it is worth.

Either you will have to keep the trimmed plates, or you will have to replace the two single gang boxes with a 2-gang box.

Good luck!