The Judge pants are a combination of leather and stretch Kevlar material. While similar in design to modern motorcycle riding pants, they were custom sewn for the movie production. You cannot source the exact same pants from an existing vendor in the retail market. You can find similar designs out there, but you will not find the "exact" pants.
There are 4 types of leather used on the Judge Pants:
The signature look to the Judge Pants is a stretch Kevlar "T" comfort panel sewn into the groin area. This material looks like suede in the movie, but don't be fooled by all the dust and distressing in the fibers, it is a stretch material with the 'rough' side showing.
The movie used suits all had urethane rubber Knee Pads, which were cast off a master pad that was made in Rob Allsopp's costume shop. The Knee Pads are stitched to the Hero Pants. We matched Pantone #334 for a close green color, it is applied extremely lightly to the surface.
On the stunt costumes, the kneepads are attached to the outside of the leather suit. Possibly held inplace by Velcro.
Below the kneepad is a Carbon-Fiber embossed leather flap (similar to the flap below the elbow on the jacket.)
In the back of the pants there is an accordian-ribbed leather panel stitched along the belt line. This stretch panel has a zipper along the top of it and it allows the pants to be zipped to the jacket. The zipper keeps the pants secured to the jacket to ensure full-body protection, and the accordian panel stretches when pressure is applied to the areas while the wearer mounts and rides a motorcyle. This is a common feature in modern-day motorcycle riding gear.
Currrently there is only one leathermaker who is offering accurate-style leather DREDD pants to the fans (Male and Female!!!). LeatherNext.com they are very fast with delivery and offer a great product.
FYI - if you are on ebay, and run across a Reel Images Leatherwear jacket, pants or vest that will suit your needs, they are a good buy. RIL developed the first accurate suit for the fans, but they had to close shop due to manufacturing delays.
If you are lookng for something a bit more affordable, and fast to acquire... the Joe Rocket "BLASTER" pant has a "T" Shaped Groin Panel and Accordian Leather above the knees. Next choice would be Xelement's "racing" pant, which only has the Accordian Leather above the knee. Both can be purchased at various places around the net, including Amazon.com.
Female pants are a bit harder to find. Skin tight, leather with spandex/kevlar stretch material. Not impossible to find, but not cheap either.