Those indicator self-cancel tabs always seem to snap off. I have just found they are available on Ebay from Jorily for £1.99. Jorily also has the entire switch but as I'm a bit skint and already have a spare switch I decided to just go for the tabs. I have looked at my spare and all you need to do is undo the two screws on the front, the case comes off and it should be pretty self-explanatory from that point on.

I have also just found that on the switch covers which pull off, you can push the bit which shows the switch type out and push it in to another and it seems to adhere reasonably well. Hence if the back of one of your switches snaps, you can simply swap them around (probably for a less used one like hazards) or find a spare and swap around.

Just done this, and when steering in the direction of indicating the thing makes a loudish click noise on the tabs. Not troublesome but I wasn't expecting it.