Hi and welcome to the forum. Aluminum will only work for a short period of time. When designing lasers our engineers would use the alum as a substrate and make custom reflectors. They went over the alum exposed to UV. We used a company that makes the reflectors used in flashlights.
I'm not sure what country you are writing from. I would talk to some companies in the reflective metals industry....discuss your requirements including cost.
Good Luck...sounds like a great project to help a lot of people.