For my research purposes, I am wondering how many horizontal branch (HB) stars are within 2 kpc of the sun? I tried to find some with the Gaia DR2 data with a magnitude cut that leaves HB stars out if they're beyond ~2 kpc, and there were surprisingly few unambiguous HB stars, so I'm just wondering how many there are and/or how to go about estimating that.
You could try selecting them in an absolute magnitude versus colour diagram.
e.g. Use the apparent G magnitude and parallax to find absolute G magnitude and plot this versus a colour ($B_p-R_p$).
The HB stars occupy a reasonably distinct region (box?) in this diagram.
Your problem is that this distinct box is blurred by differences in composition and by extinction/reddening. You could sidestep the latter to some extent by avoiding low Galactic latitudes.