Thunderbird 900 Keihin Carbs

I have been suffering Carb problems with my 2001 Thunderbird 900 for a good few months now. I've had great response from folk on this Forum but sadly the problems persist. Stuttering at low revs, cutting out completely at times, and the only way to keep the engine going was to keep it above 3000 rpm. Not recommended in traffic.
I handed the bike to a Carburetor specialist who stripped them right down and found that they are, " beyond economical repair due to excessive wear ". The bike may be 20 years old but only had 36000 miles on the clock and is in general good overall condition.
I've tried to locate replacement Carbs but there doesn't seem to be anything suitable. What I have traced is either poor condition, or exorbitant prices with no guarantee of working order.
Can anyone help ; there must be something suitable out there, even off another Triumph triple.