TowSmart Class 5 5/8 in. Barrel Style Receiver Lock 4 in. Span fits 2 in., 2-1/2 in. and 3 in. Receivers 7279 - The Home Depot
Amazon.com: YITAMOTOR 4-Inch Hitch Receiver Pin Lock with 5/8" Diameter, Extra Long Stainless Steel Trailer Hitch Locking Pin, Fits Class III IV 2" & 2-1/2" Receiver, Silver : Automotive
CURT Coupler Lock (1/4 in. Pin, 3/4 in. Latch Span, Padlock, Brass-Plated) 23501 - The Home Depot
Unique Bargains 1/4" Hitch Pin Lock Trailer Hitch Lock Trailer Hitch Receiver Set Gold Tone for Car - Walmart.com