The link below has a file within specifically related to your hitch. With early models of the 3, the "plow" did not come standard - you had to purchase it extra; also there were key lock problems with the early units as well - referenced below.
In theory, you can find the "plows" on eBay; I would recommend you purchase the newer shorter LR4 style.
The picture within the link shows the original 2005 model "plow" for the LR3 and the newer shorter hitch "plow" introduced with the LR4. Either plow can be used on the LR3/D3; they are interchangeable.
The part number of the newer third generation short style is LR019990 replacing previous long type part number KNB500080. There were two versions of the longer one, KNB500080 with the orange key, apparently a better locking setup. The first generation, KNB500023, with a black key was less than perfection.
The green lock assembly with orange key, part number KNW500010, shown on the shorter hitch, can be purchased separately should a key be lost.
Regardless of receiver model, the receiver will accept nominal NAS 2" tongue on which may be mounted the appropriate ball size.
http://www.disco3.co.uk/gallery/thumbnails.php?album=4497