Thread 3 shrimp and 3 pineapple cubes onto each of 24 skewers. Simmer orange juice, honey and sriracha in a small saucepan, whisking until smooth. Add cornstarch mixed with 4 1/2 teaspoons water and whisk over low heat until sauce thickens. Grill 1 skewer per serving until shrimp are cooked through, remove skewer from heat and brush with 1 tablespoon orange juice mixture.