Again, as Fungus already asked, what meter are you calibrating?
Most current meters measure the voltage over a shunt resistor of some known value, and you can do the same, except by using a higher value shunt resistor. For example, with a 10Vac test signal and a 100Ohm resistor (inclusive wiring and the shunt in your DMM to be calibrated) you get a 100mA test signal. Then measure the exact voltage over the 100 Ohm resistor to get the current, and adjust the DMM under test to display that same current.
You write you don't have an AC source, so get some (half) decent function generator, and maybe combine that with some audio amplifier.