I think you may be referring to POR-15. While I have never used it, the reviews I've seen indicate this is a great product. In my research to obtain via Internet, I found the product expensive to buy and then ship.
A friend suggested I try a local automotive supply store called FinishMaster. They are a chain that caters to professional auto body repair. The clerk there turned me one to an alternative from SEM called Rust-Shield. While he had both products on the shelf, he recommended Rust-Shield and it was cheaper. Over the past three years I've painted various metal things with Black and Aluminum colored Rust-Shield and have been pleased with the durability of the product.
Whichever you choose, go to your local automotive supply store and check options - you will get a much better paint than the local big-box provides.