Can I do this by just changing the chain rings? And where can i find campy chain rings?

no...

Think about it.

Chainrings with fewer teeth also have smaller diameters. As yu reduce the number of teeth, the diameter of the chainring will eventually decline to less than the bolt circle diameter that holds the chainring onto the crank. With a typical 130mm BCD Shimano double crankset, the smallest chainring that will fit is 38t. Campagnola is even worse because Campy uses a 135mm BCD.

thanks

I read in a similar thread that, although they may be hard to find, there are standard (53/39) chainrings that will fit a compact spider but, for the reasons stated gouchily in an earlier post, no compact rings that will fit a standard spider. Since you'd need to remove the crank to change the chainrings anyway, you might as well have the two cranksets that you can just swap out when needed. You'll just need to adjust your front deraileur height and cable.

NP

You can't really get all the way there, but you can get close... Stronglight makes BCD135mm rings in 50/38 (you can actually get as small as 48 outside, but 38 is the min. inside since you can't make a smaller ring with 38teeth)

^ That doesn't bring you close to the 34 I have on my compact crank. Without that, the only people who would care about a 50 or 48 outer would be junior racers on gear restrictions and people on 5 speed rears.