Can you even get smaller chainrings for the Campy? The BCD is 135/74 mm and the selection of outer rings will be quite limited. For example, the only 135 mm chainrings Harris Cyclery lists are 1/8" track rings and their reference to QBP's chainring selection is no better
Shimano road cranks use the more common 130 mm outer BCD and there are more choices. If you can find an older 9-speed Ultegra or 105 triple crank with the Octalink bb, you have a large selection of rings and these are available at much lower cost. The 105 was available in 50/39/30 configuration.
BTW, a 26T chainring can be substituted for the 30T on any crank with a 74 mm bcd granny ring. I've done this on numerous Shimano cranks and even on a 10-speed Campy Chorus triple crank and it works very well.