Light Switch

Measure the hole for the switch, and search for a snap-in switch of the right type that fits the hole. There's a fairly good chance it's standardized. Ideally you want a switch that's rated for DC use. (The last line embossed on the old switch says that it's rated for 3A at 14 V DC; the solid line with the dotted line means DC, while a squiggly line means AC.)

There's no need to find precisely the same model number of switch so long as the physical dimensions and electrical ratings are acceptable. I suppose finding one that's whitish would be preferable aesthetically speaking.

Places like Digi-key and Mouser, among others, sell very many different brands and styles of switches.

I didnt search Cole Hersee but you may find it on their site.

Cole

These two companies offer after market switches. You should measure switch opening for proper fit.
JR products

RV Designer

I bought a couple just like that at a RV dealer in Branson, MO. From that, I just figured that it was a common thing to find. Maybe not with the on-off marking. Maybe someone else will come up with a solution.