Where to buy a used metal lathe

craigslist might have something in your area, otherwise check the local yellow pages for used tools. Sometimes people are getting out of/changing whatever hobby would use a small lathe, try the local metal workers and wood workers for connections.

Without knowing where you are and how far you are willing to go, it's a very difficult question to answer : )

Do you know what accessories you want/need? What can you make or improvise? Turning pen blanks is different than turning firing pins is different than making gears is different than winding armatures...

Harborfreight has some, here is one.