What generals are you thinking of that are raising legions out of their own pockets without senatorial authority? Catiline and Manlius did so, but their troops were in open rebellion and were likely not paid and provided for normally--Catiline could not mint coins, after all. Generals during the civil war? I think it's pretty silly to talk of senatorial approval for imperium during the civil war. Even then, the Republicans before Philippi were unable or unwilling to pay for their army and resorted to collecting funds, often by duress, from eastern cities. The Pompeians resorted to a similar tactic (much of their wealth, like that of the Republicans, would have been locked away in Italy and confiscated by Caesar), confiscating money left behind in the east belonging to, among others, Cicero. Who are you thinking of exactly who's raising self-funded armies without senatorial approval? Sertorius? Any example I think of is unusual, an individual in revolt or in open civil war.