Loving my NC 3.5, but feel those side indicators/repeaters are just massive and out of character to the rest of the car!
Are there any alternatives or replacements?
TVM 
They are the same I think as used on the NA/NB. There are alternatives, I think from the old Fiat 500, from the likes of Zoom Engineering, or DIY after finding some suitable repeaters from a car parts catalogue. Of course, the old timey look might also not be in keeping with the NC.
https://www.mx5nutz.com/threads/show-me-your-side-repeaters.292705/
You don’t say which type you have, are they amber/orange or the clear type?
I have the clear type as standard on my NC 3.5.
From this you now know that there are two options and you may like the opposite to the colour that you have.
Richard.
Thanks Richard. They are the clear type, but just seem so big!
Also this (monstrosity I think)
https://www.jassperformance.com/shop/side_indicators
Anything for the NA/NB will fit the NC.
Funny how tastes differ. I quite like these! 
As my Pop used to say, “It’d be a very boring World if we were all the same!”