It should be the same list of locations, including the Tourist Information office in the train station, or the one at Via Cavour (this one says credit card only, per p. 488 in Rick's Italy book), the back entrance of Santa Maria Novella (also near the station), and several other locations. For your larger group, the certainty of paying by credit card may be enough reason to buy it online.
Of course, we advise travelers to be prepared with cash for most situations and that includes families and larger groups who often need large amounts of cash in their money belts. Do check/increase account withdrawal limits for those people who will be responsible to carry the funds. Deustche Bank branches will allow large ATM withdrawals, if your own bank also will.