Simple 3-sparkle pixel brush!
The sparkles adjust with the brush size, so you don't have to worry about doing math to make sure the particles look right if you make the brush bigger- but!
The first particle must always be a multiple of 3, which makes 3.0 its MINIMUM size
If you want to change the spray range (Brush Size) and particle sizes separately, open up the advanced settings and uncheck this box:
AND this box: