Hi there!
I can imagine why you use a brush to apply the paint of the spray-if I'm not mistaken,you just like the specific paint,so you spray on a piece of plastic for long time,until you get a good amount of liquid paint,and then you dive your brush in it,right?
Anyway,do not do this!This kind of paint are hard to be removed!If the spray is a kind of acrylic,you could clean your brush in NitroCellular Dilluter.You could buy it from a shop with house wall paints.This dilluter is a must for a modeler,it can remove paint from metallic models!But it may destroy your brush!So,if the paint is not removed quickly from your brush(in a few seconds...),I don't know a way to clean your brush having it damaged in a minimum level...
In any case,take the spray with you at the shop.The seller of the dilluter may recognise the type of the spay paint by the smell,so he or she may propose a more specific diluter.
Good luck!
-Kostas.