I have downtube shifters--10-speed Dura Ace--on my Serotta. I've never had integrated shifters at all, so I figured, "why start now?" Shimano makes both downtube shifters indexed for 10-speed and brake-only levers still. Though they're both a bit high for what you get, they're still cheaper than the alternative.

Campy is still making bar-end shifters for their groups, and luckily, the bar-ends are essentially the downtube shifters with a different mount. You can pull the shift levers out of the mount and reinstall them with the proper stops on the downtube. This is an expensive option, unfortunately, as Campy is very proud of their shifters. LeTour makes a kit to ease this conversion, but it's become about impossible to find. The simplest and possibly cheapest thing to do is find a set of older indexed shifters cheap and add the index wheel from a 10-speed set (obtainable from Campy).

Good luck!