It’s not that rare. One blimpful would do for a whole lot of scoundrels, especially if you recovered as much helium as possible after the festivities.
Just off the top of a google search, here's a short article excerpt:
The cost and supply of Helium has caused chromatographers to use Nitrogen gas generation as a cost effective alternative. Helium has been used as makeup gas in gas chromatography for decades, but the global shortage of helium has caused costs to skyrocket and availability to decline. Helium is an inert gas generated by the radioactive decay of thorium and uranium. Trace levels are found in the atmosphere and higher levels in natural gas fields. ...