The service limit of the four clutch springs is 32.5mm – anything below this and the spring should be replaced. A new spring should have a non-compressed length of 33.9mm (1.3346″).
Easiest method to measure them is using calipers like in the above photo. As you can see, the spring being measured is just outside of the service limit and should be replaced.
We like the EBC springs – you can find them on eBay! The original Honda part number is 22401-415-000 – you can also try an eBay search for those. Need new plates as well? We like the EBC kit for the CX500s too – eBay link. Note that the Turbo and 650s use a different kit.