How to get power to a fan?

Okay, i didn't know where else to put this, so here it is. I have an external hard drive box that i built myself, and i want to put some fans in it, but it doesn't have a power supply. each of the drives has its only power adapter, which i have linked together going out to one power cord. I really don't want to put a fan in, but i don't know how i'd power it. Any ideas?