I accidentally threw my master ball on a Snorlax , thinking it was a heavy ball. Unfortunately, it was too late to do anything about it. Is there a way I can get another master ball?
Yes there is. In any Pokémon Center, there are Rotom Information Terminals which give you the option to play the Loto-ID. If you match all 5 digits (which correspond to the last 5 digits of a Pokémon's ID), then you will win a Master Ball.
Source: https://m.bulbapedia.bulbagarden.net/wiki/Master_Ball