I saw the roshei teivos החזו"א in the Dirshu notes to Mishna Berura in Hilchos Rosh Hodesh. Can you tell me who it is? Is there a general resource to figure this out?
I suspect that that refers to the Chazon Ish. The letters fit, and the Chazon Ish's rulings are often quoted alongside those of the Mishna Berura.
I know I'm a bit late to the party here, but for anyone who views this answer in the future: There are a couple of resources you can use for roshei teivos: If you want to look online, you can use this page; if you want to actually hold a sefer in your hand, you can use this kovetz roshei teivos (I have it and can personally attest to its tremendous usefulness).