I've recently bought a 2000 Ford Ranger. The 4x4 didn't work I took it to a shop and they said that the Electric Shift motor was missing.

Does anyone know if I can buy an aftermarket one and were?

Look on e-bay. I'm not sure about your year, but I have an 86, the motor for mine is there. Do a search for "ford ranger shift motor" you should find it! ( mine was $199)

You could also get a decent used motor at your local junkyard. No shipping costs and you can get it fixed quicker.