Pepper spray is a great non lethal self defense weapon to have either to carry with you everyday or store in your home as well. There are many great options out there in varying sizes.
But I would strongly recommend against a pepper spray gun! These have been easily mistaken for real guns and in a dangerous situation you do not want to pull out your pepper spray gun as the attacker will react to seeing a gun shape and could shoot you first, or worse still even if the attacker does not have a gun - Someone with concealed carry across the street may see you pull it out and think you are about to shoot them and your the bad guy and shoot you!
Here's a link that discusses a a selection of
small to large Police Magnum pepper spray canisters. All of them contain the maximum heat strength allowed by law:
What pepper spray is the best ?
Stay Safe