There are 2 pre-drilled holes on your dash- one for overdrive and 1 for a heater. If you don't have one or the other
of those accessorizes, you can use those holes in lieu of an extra bracket. The Lucas push-pull switch, similar to
your wiper switch, is quite often on eBay.
Moss, TRF and NOS Locaters sell an aftermarket version which is quite similar to the Lucas ones, but the bezel is incorrect. It's
chrome but has a period look if you're not fussy. As Randall says, sand down an extra knob that you might have, but better yet,
fill in the letters w/JB Weld, body putty or whatever you have. Then sand it & paint it.