Radio Servo Extension Cords
Make your own. Get some shorter extensions and insert wire into the extension to make it the length you need, then add in the other two connectors to make your 3 to 1 harness. Please tell me one of the leads will be used for a separate battery pack. If not, driving 3 servos from a single power source, your receiver, is just asking for trouble. Especially if this is for a large model, which I assume it is since you need it 48" long, where servo/power loads can be quite high.
John