Aerosols are hard to get shipped anywhere, and I use them rarely. I don't know of any Belgium online stores, but you might try:
http://www.sockelshop.de/catalog/index.php?language=en
I have ordered from them a couple of times, and they where very fast. Had my stuff in a couple of days, and delivery to Sweden is probably slower.
They don't seem to have the Model Master spray paint, but they carry the the normal paint, so they might be able to get it for you, and ship it by train.