Campy produced many versions of their Gran Sport cranksets. Their 3-arm versions (aluminum and steel) were designed around older 116 BCD standards.
The chainring bolt holes on those cranks were 9mm rather than the 10mm of their 5 arm spiders. That means that you will need 9mm bolt-hole chainrings and matching 9mm bolts. If you can't find original bolts, then TA Pro-3 bolts will work.
The other peculiarity of these cranks, is that the crank only has chainring shoulders on one side of the spider (a-la pista cranksets or older 3-arm cranks). So the smaller ring must be mounted on the larger ring or you'll need to make your own bolts washer combination to enable mounting smaller independent inner rings.
If weight is no object, then Cyclo steel ring sets will work. They are available on ebay regularly and very reasonably. They go down to 36 teeth, but are available in many combinations. The advantage of these chainrings is that they will last forever (they wear out the chain rather than the other way around).
Campy original equipment is available but only down to 42 on the inner ring. And they're not cheap.
Photos at: http://www.flickr.com/
Amir Avitzur
36 tooth inner ring fan in R"G Israel