You can buy watermelon liqueur which tastes exactly like the jolly rancher flavour (my personal favourite). If there is a Moxies anywhere near you they used to have martini nights and one of their drinks was made from this liqueur.
Cruise T&T or anyplace with a good selection of Chinese and Japanese canned and bottled soft drinks.Some of the Japanese Raimune-like bottled drinks are melon-y flavored.