The Coast Guard Uniform Regs state..."the Hot Weather Uniform includes ODU shorts hemmed at the knee or 1 inch above the knee". In the past, you had to kill a good pair of ODU pants and pay someone to hem them as shorts, but now you can buy shorts commercially.
Propper, Inc makes my Hot Weather Shorts -- they're the exact same material, style, and construction as ODU pants (which Propper makes for the UDC), and so are as close to an official pair of "ODU Shorts" as you can get.
Note: Please check with your chain of command before purchasing these shorts -- if you buy them and aren't allowed to wear them, I'm not going to cry for you.