Check out the Narva website under rocker switches.
The Narva Rocker fog lamp switch listed under the standard duty section slotted straight into one of the lower row of holes in the centre console of my Mav. http://www.narva.com.au/products/browse/standard the opening si2e listed is 34.5mm x 20mm.
I know you want momentary on or momentary off. these are also listed on the Narva site under Rocker Switches heavy duty but the opening si2e is bigger at 37mm x 21mm.
http://www.narva.com.au/products/browse/heavy-duty-3