Two different farm supply chains (Blain's Farm and Fleet and Tractor Supply) here carry Valspar enamel colors. They also carry their hardener. I have used it on several items including my Bridgeport mill as well as three different vises I have rebuilt. It's good stuff, making the paint harder and causing it to cure more quickly. It adds gloss and makes it flow better too. Enamel usually cures very slowly. The hardener will not make it rock hard the next day, but certainly dry to the touch and not soft the next day. It will quit smelling like solvent within a week or two rather than continuing to off-gas for months or years as is normally the case and is very hard at that point.
The instructions are for mixing an entire gallon...but a little calculation will help you determine the correct ratio so you can mix small batches at a time. The only annoyance is that you have to stir the mix off and on for 30 minutes before you begin application.