There are definitely shorter chainring bolts available, I don't know if campagnolo makes the correct size (2mm shorter than your current one's) though.
You could try to grind or file down the female part of each chainring bolt by approximately 2mm. This wil enable you to screw in the male part of the chainringbolt further which will enable you to correctly clamp the chainring(s) to the cranck arm. You might need to clean up the threads in order for the male/female parts of the bolts to easily thread into eachother.
You could alternatively use something like this: https://www.universalcycles.com/shopping/product_details.php?id=59276
I have seen similar spacers on an old shimano 600 cranckset.
there are also so called 'chainline spacers':
The same effect could be achieved with appropriately sized washers though (which will be a cheaper option).
You can choose from various chainring bolt lengths on this website:
Cheaper chainring bolts in multiple lengths:
PS: iirc you only need to replace the 'female' (threads on the inside) part of the chainring bolts with a shorter version, you could potentially keep using the original campagnolo 'male' parts which might be desireable such that you keep the campagnolo branding on your chainring bolts. Using the original (longer) 'male' parts will however make the thread stick out approx 2mm on the back of the inner chainring (when not using shims/spacers/washers).
If you could measure the thread length on the chainring bolts you currently have I could find you some suitable (2mm shorter) chainring bolts.
I hope this helps.