Front derailleur clamps and clamp-on adapters for braze-on type derailleurs come in three diameters of 1-1/8" (28.6 mm), 1-1/4" (31.8 mm) and 1-3/8" (34.9 mm) so your frames are one of these three sizes.

I have a very lightly used 105 braze-on 8-speed triple front derailleur intended for a 52/42/30 crank. It's yours for the asking. PM me if you want it

You will need an adapter clamp of the correct diameter but any LBS should have them and Nashbar offers them at a very low cost.