These are shark-infested waters you're bathing in here, George ..

. For some reason, certain people seem to get very wound up about production figures, asserting all kinds of things as if they were Gospel and maintaining that all disbelievers are heretics who should be burnt at the stake.
Nevertheless, I'll risk getting my toes wet ...
IMO, Ian Falloon is STILL the best source of information about production figures. At least Ian has examined the factory records - in fact, as I understand it, he himself discovered a cache of them at Bologna when everyone thought they had been lost or destroyed, either just over the normal course of time or when the Castiglionis took over.
So what does Mr. F have to say?
For the 250 Desmo, he says that the total production of the 239 and 250 Desmo during 1973-74 was ... 727. And of those, 277 were 250 Desmos made in 1974, the year of the disc brake. P.s. All the post Silver Shotgun 250 Desmos were yellow, as far as I know.
For the 350 Mark 3, the blue and gold model only: well, it appeared in 1973 and went on to the end of 1974 (even if it was still available in the shops in 1975). For those years, Mr. F. has production figures of 476 for 1973 and 324 for 1974, making a total of 800 bikes over the period.
HTH
Craig