|Used switches appear on eBay occasionally, and I've seen a couple for sale that claimed to be new old stock. Other than that, new original style switches seem to be unavailable. What you can do is order a replacement from Delta Motorsports. These look a bit different, and have blade contacts rather than the pins of the original. To use them, you would have to either (a) replace the original wiring harness connector with the blade receptcles Delta provides, or (b) use the blade receptacles and the back portion of the old switch to create an adapter between Delta's switch and the harness connector.
The headlights and fan switches are identical save for the legend stamped into the rocker of the switch, so if you have a spare switch of the wrong type, you may be able to swap rockers between the two switches and get what you need. This does require considerable caution as old British plastics tend to be very brittle.
The bulbs for the three warning lights on the heater console should be available from any British parts supplier. For the housings themselves, try Delta Motorsports -- and if they don't have them, probably the only remaining source is eBay. The only difference between the three housings is the film containing the legend text, and the housings themselves can be disassembled if you're careful, so a spare of one type can be turned into a replacement of another.