If you google "2k urethane clear aerosol can" without the quotes you will get a bunch of manufacturers and distributors to pick from.
It is a REAL urethane clear that I have tried and it acts just like the "real thing" shot from a gun. I am concerned though about spraying anything over your rustolium, there is a good chance it is going to lift. Get it warm and don't spray it on too heavy until it has a few coats, then spray it a little wetter. But testing it would be highly recommended. Problem is, that clear is $20 a can.