That's right! You can easily get a "RETURN TO SENDER. ADDRESSEE UNKNOWN" rubber stamp from Rubber Stamp King.
Rubber Stamp King also offers custom stamps, so you can create a stamp that says exactly what you want it to say. This is a great option if you have a specific message in mind, or if you want to add your company logo to the stamp.
Ultimately, the best type of "RETURN TO SENDER. ADDRESSEE UNKNOWN" rubber stamp for you will depend on your individual needs and preferences. Consider the size, type of stamp, and ink color that would be most useful for you, and then browse the selection at Rubber Stamp King to find the perfect one.
I hope this helps!