The Meaning of Life, the Universe, and Everything.
try /summon and then hit 'TAB' until mammoth shows up. perhaps find the mod name and try it.
something along the lines of /summon DrZharksMoCreatures:Mammoth [idk what it actually will be but it will be like that]
or you will have to just spawn elephants in vanilla taiga and golden lasso them to where you want them. if you don't have a golden lasso or don't want to install extra utilities, you can use mcedit to create a 2x2 taiga near your base.