We do golf
signs in full color all the time, in square, rectangular, and round. Since we have the equipment, we flatbed print the coroplast, and then if the order is for round or round with a "tee" we cut the printed sheet on the router.
Printing is a great way to go, since you can layout your base design and the sponsor text on each individual
sign, so when printed, the finished sig is ready to deliver.
If you don't have the equipment, find a good wholesaler, lay them out, send them out, and make yourself some money.
happy Signing!