This isn't exactly DIY (not sure if that was what you are aiming for), but Scheme Designers could help. They've designed my future paint scheme for the RV-10 and delivered the instructions so a paint shop can create it. At the time they delivered, I also had the option for custom-cut masks or vinyl markings. A tad expensive, though well worth it for what I wanted. Again, not sure what the scope of what you're looking for. I am sure that a paint shop might also be able to help you in a cost-effective manner if you are not looking for something elaborate.