That's a very good question. I went looking for a source that might give an estimate and couldn't find anything. I found LOTS of sources that describe the difference between Population I and Population II stars. Here's one of the better ones.

Pop II are the old "first generation" stars that we're talking about here, but the two "populations" really grade into each other with a full range of intermediaries. Sounds like neither group is rare, but I couldn't find an estimate of the proportions of the two groups.

Perhaps the reason I couldn't find such an estimate is because it would be difficult and pointless to develop one.

Difficult because the brightest stars we see are all young and therefore Pop II, because big bright stars don't live long. All Pop II stars would be dimmer than the sun except for the few that are currently in the red giant stage. Also, since Pop I stars live in the Galactic disk, and Pop II stars live in the halo, nearby stars are mostly Pop I (like the sun). Any astronomer would recognize that both those differences would bias any survey toward over-estimating the proportion of Pop I, so it would be difficult to find ways to account for that bias.

Pointless because there is no clear line between Pop I and Pop II - they form a continuum, not two groups - pick your dividing line and you can make any number come out right.

Or maybe I'm just stupid and the next link I checked would have had it.

Here's a link about an extreme Pop II star.