Ahhh unfortunately while some years ago you could buy band-on downtube cable stops with integral cable adjusters, I haven't seen them for sale for years. So afaik what is available in your case is something like
this, with no cable adjusters. While no adjuster is usually ok for the rear mech (because rear mechs usually have one), it could be a bit of a pain for a front shifter which dosen't have an adjuster (because front mechs practically never have one either).
Theoretically an alternative exists by sourcing a pair of suitable downtube band-on shifters from e.g.
ebay which
hopefully has the right sized bosses to fit something like
these after removing the levers, but it IS a tricky endeavour.
I guess if the frame is steel it is conceivable that what is broken could be brazed on again.
I hope what I wrote here is proved incomplete by someone.