Considering Trump is widely hated throughout ALL DC agencies and contractors (since he threatens their lively-hood)), anyone at a tech level comparable to his could access it before the masking process. Everyone in DC reads the WaPo, and knows who their reporters are. Those reporters (and many others) are begging for any dirt on Trump or any of his people.
THAT, IMHO, is how the transcript got to reporters. Probably shopped around till someone bit, too.
Plenty is not a very big number and it is all traceable.