I actually purchased my half-mask respirator from a hardware store a few years back. I even bought the refill cartridge back then. You can just look around in a hardware store and ask for one. But have to make sure you got the right catridge and just do a lot of research.
Just like you, I also just held my breath before and just spray, then rush the heck back into the house and finally breathe. When I first started doing face-ups a few years back, I would use the respirator but then I got pretty lazy and just did the whole daring feat of holding my breath.
But just like you too, I read the whole DoA thread about the respirator and got myself paranoid. Lmao! But anyways, I purchased my mask from a hardware store in Sunway Pyramid previously. I am sure you can find one in any hardware store really, mainly in the shopping malls.