Well, if your only goal is to hire a unit of elephant mercenaries, you need to do two things. First, make certain it's at least 25-50 turns after the development of gunpowder. Second, put the general on a boat and head him down to the middle east. Both types of mercenary elephants only have a single unit available every 25-50 turns. If you get over there, and if the unit is available, then you can hire it and drag it back.

Now, if you just want the unit, use two cheats:

First, use
Code:
create_unit London "Mercenary Elephants" 1 0 0 0
followed by
Code:
give_money -2750
That should bring a unit of elephant arquebus mercenaries in London, and subtract the 2750 florin hiring cost from your treasury.