The photographer I used to assist for coated his photographs with a laquer spray he purchased in gallon-size cans. But, he had an expensive setup complete with a ventilated and fully equipped paint booth.
Here's a company that sells a similar product in spray cans;
http://www.mcgpaper.com/yourmemories.html I've never used the stuff like this that comes in a spray can, so not sure how good it is.
One word of caution: Many labs now are using pre-coated media that sometimes doesn't play well with spray coating. I would definately experiment before spraying anything on your good photos.
