there are other options for cable stops..

Search: Vintage Suntour Cable Guide Barcon Housing Stop Down Tube Clamp On 28.6 SUN TOUR
or: Vintage Shimano 333 Dual Cable Down Tube Clamp On Barcon Housing Stop 28.6 mm
Co-Ops usually have several of these stashed away....
and there will also be Huret, Simplex, and Campagnolo options too, i'd venture...
these were mostly used for Stem mounted shifter bikes, but then Bar ends came into vogue... my second road bike had bar end shifters, and the needed stops clamp too... 1970.
Sometimes, i still reach for the bar end while riding my drop bar CF Brifter bike.

Many use a clamp-on Shifter boss with the Adjustable cable stops shown in your post, too.

measure your downtube to verify tube diameter before purchasing any clamps.