Hi Marcus,
Greetings from Scotland.
are you wanting a Sinclair Indicator kit or do you want to make your own?
I have a set of LED indicators fitted. I got my own 12v LED relay for a motorcycle and on-off-on switch and front and back LED Amber lights. I just fitted them as per the instructions you'll find in the on the C5 Alive website using the wires that run up the tunnel on the C5. You could use normal lights, but the flasher relay would need to be a normal 8W one.
They work fine, and it only cost about £20.00 for the whole lot,( 23 Euros). I did have the bracket for the switch, but you could make one that fits from a bit of steel or aluminium plate.
Cheers John