For anyone interested I found some Wyeast 2105-PC at altitudebrewing.com in Denver, CO. I've never ordered anything from them, but they do have a wide selection of brewing paraphernalia. Prices seemed a tad high, but not out of reason.
One thing they do carry is a yeast brand that I'm not familiar with called Propagate Lab. I get the feeling their main customer might be commercial breweries, but they have a very detailed downloadable .pdf cross-referencing their yeasts with other common yeasts, along with the supposed origins. According to their chart, there are actually (at least) three Chico variants, two of which are allegedly common to Sierra Nevada and one common to Stone. That seems to support the spreadsheet data that D.M. Taylor compiled from numerous sources.
Anyway, the chart is worth perusing even if their yeasts don't interest you, but they claim to have 2x the cell count of Imperial and 4x Wyeast, for $12. Worth a look-see.