What are some common ways that I can vaporize Metals into a vacuum chamber? How can I keep these Metals in a gaseous state?
The easiest way to vaporize a metal is to create a filament of the metal. Heat the filament in the vacuum to its sublimation (vaporization) temperature. Alternatively, when the metal cannot be shaped into a filament, the metal can be encased in or painted on a "wrapper" metal. Commercial evaporators for alkali metals are designed this way. The wrapper is a thin tungsten foil encasing the alkali and having a small slit or hole in it. Heat the wrapper, and the alkali evaporates.
As to keeping a metal as a vapor, consider how to confine a metal within chamber walls AND keep it as a gas. When the walls are colder than the sublimation temperature of the metal, the instant the metal gas hits the walls, it will condense. So, as already noted, the chamber walls will have to be at least as hot as the sublimation temperature of the metal itself, if not hotter.
An alternative method to keep metal "gaseous" is to ionize the metal immediately as or immediately after it is vaporized. The metal ions can be confined within a magnetic field.
The methods to vaporize metals are relatively cost effective, well-documented, and reliable for small amounts of material. Vaporizing more than nano-gram amounts of metal heads to expensive, professional-level designs. The principles remain the same.
vaporizing metal in a near-vacuum is a straightforward process; the simplest method is called sputtering and is one specific method of vacuum metallization as noted by William Hird above.
Keeping a vaporized metal in a gaseous state for more than a few milliseconds is a different proposition, however. For that you would need a furnace with tremendous power and extremely good insulation surrounding it.