In a large bowl, combine crab meat, 1/2 cup panko breadcrumbs, mayonnaise, eggs, red bell pepper, green onions, Dijon mustard, Old Bay seasoning, black pepper, and cayenne pepper. Mix gently to avoid breaking up the crab too much.
Form the mixture into 1½-inch balls (about 32 balls total). Place remaining 1/2 cup panko in a shallow dish and roll each ball to coat lightly.
Heat a large skillet over medium-high heat. Working in batches, quickly sear the crab balls for about 1-2 minutes per side until golden (they don't need to be fully cooked, just lightly browned).
Line your slow cooker with parchment paper. Arrange the seared crab balls in the slow cooker and drizzle with melted butter.
Cover and cook on LOW for 2 to 3 hours, until the centers reach 160°F (71°C). Switch to WARM only after the crab balls reach that temperature, then serve with toothpicks, lemon wedges, and remoulade sauce.