If I read the original posters situation correctly, the frame has brazed on shifter bosses and he has a complete banded clamp on down tube shifter assembly.
Depending on the brand of the assembly I would go with shifters designed to fit the braze ons, for Campagnolo or compatible shifters cutting those apart will get you 90% of the hardware you need, only a thick washer placed inside the lever will be needed.

Way back when braze on shifters started to become the "in" thing, plenty of guys drilled out the back side of their Campagnolo shifter clamps and harvested the cable stops, only needing the mentioned thick washers to get it all to work.