I know there are a couple of MX markets in Manassas. There is a large one near to Taqueria Tres Reyes. Actually mero mexicano and not Central or South American. I can't say for sure if they will carry hoja de aguacate, but they might, as it is not an atypical ingredient to have in a MX grocery.
I was just reading a Mexican cookbook and wondering this myself.
The Etsy ones look interesting.