Commercial atomic clocks of various types aren't that rare. Every cell site has a rubidium standard and/or GPS timing, many data centers probably have a cesium

Commercial atomic clocks of various types aren't that rare. Every cell site has a rubidium standard and/or GPS timing, many data centers probably have a cesium standard, and radio astronomers use H-masers for interferometry. Everybody with a GPS-disciplined oscillator has access to time and frequency from the Naval Observatory at the sub-100 ns level, optionally augmented to +/- 1 ns with reasonably affordable gear like https://www.sparkfun.com/sparkpnt-gnss-disciplined-oscillator.html https://www.sparkfun.com/sparkpnt-gnss-disciplined-oscillato... . A fountain clock is on a whole different level than any of these. The same researchers who build fountains also work on even better optical lattice clocks, none of which you can buy from Sparkfun. These are research tools that don't have a market, at least not yet. The SI second definition will likely move from Cs-133 at 9 GHz to Sr-87 at 400 THz before too long ( https://www.nist.gov/si-redefinition/second-future https://www.nist.gov/si-redefinition/second-future ), but that probably won't shake up the existing market too much.