If you are certain that you have found all the fuses and
disconnected them, also pull out any relays you can find. If the draw
is still present, then disconnect the alternator wiring (be very
careful not to let the big alternator wire ground out against the
engine or any other part of the car (it will spark). Secure the wiring
to prevent sparking.
Make sure you have all the fuses out at the same time, not just
one at a time. Some components may use 2 fuses for shared power, and
you might miss the draw unless all fuses are out at the same time. Just
keep track of their positions when you do this.
If the draw goes away when the alt is disconnected, there is a problem
with the alternator (could be a bad diode) allowing it to drain the
battery.
Obtain a wiring diagram if possible, it will usually make the diagnosis easier.