Volatile alkali metal compounds Most elements are or have compounds that are gases or have a significant vapor pressure at room temperature. Fluoride is a powerful tool for producing highly oxidized covalent and volatile compounds. Tungsten hexafluoride is gaseous at room temperature despite being made with the element with the highest melting and boiling point. Refractory elements can also have volatile oxides such as $\ce{CO2}.$

Organometallics such as iron pentacarbonyl and dimethyl zinc are liquids at room temperature but have a decent vapor pressure, boiling at 103 °C and 46 °C, respectively. Other examples of "volatilized elements" include diborane and heaver analogous of ammonia such as phosphine. 

All of the compounds I found of alkali metals, however, have very low vapor pressures at room temperature. For example, organolithium compounds tend to form lithium clusters or ionic crystals and decompose into lithium hydride when heated (which isn't volatile), rather then the covalent examples previously. Alkaline earth organometalics seem to suffer a similar problem with dimethylmagnesium forming a solid lattice.

Are there any known examples of an alkali metal compounds that has a reasonable vapor pressure, say 100 Pa at 300 K?
As Mithoron says in the comments, tert-butyllithium is one choice.  Like pure organolithium compounds generally, this is pyrophoric and reactive to many common atmospheric gases or vapors. An article by Schwindeman et al. [1] recommends using a nitrogen or argon atmosphere.

In the case of alkaline earth metals, magnesocene provides a relatively volatile magnesium compound, subliming at $\pu{100 °C}$.  This is also air- and moisture-sensitive and again, should be handled under nitrogen or argon.

References


Schwindeman, J. A.; Woltermann, C. J.; Letchford, R. J. Safe Handling of Organolithium Compounds in the Laboratory. Chemical Health and Safety 2002, 9 (3), 6–11. https://doi.org/10/ctj2sj. (PDF mirror: chemistry.ucla.edu)