n95 mask should be more than you need the ash isn't dangerous. You can buy n95 maskes from homedepot or any hardware store. If you really want to get hardcore and waste some money you could buy n100 or p100 like thisIs there such a thing and if so could someone point me in the right direction?
(not my auction)
As for gases, we would need to know what you mean by this. As i understand it the gases put off by a volcano cannot be filtered by normal mask you would need a supplied air setup. Easily place to buy these are from paint shops to use in painting booths. My guess is you wouldn’t really need this unless you live by somewhere that you plan to need a mask to get away from.
here is a link to fema valcano ash info.