Pinbits says sold out on the kit, but still have the ring. All you need then is the ROM. I'm sure that can be easily had.

https://www.pinbits.com/index.php?main_page=product_info&cPath=13_8&products_id=135&zenid=709258ad81b9643f79301cbe4aa08fab

ROM is available for download on ipdb. L-1 (with planet lock)

http://www.ipdb.org/machine.cgi?id=1322

An alternate listing:

https://www.pinbits.com/index.php?main_page=product_info&products_id=8

There are different colors available. I saw a game for sale a while back with a blue ring installed, which looked interesting.

Usually if you email and ask about a product that was out of stock, they'll make one for you.

If the locking ring is your go/no-go factor on the game, it's not too hard to find, even if pinbits is out of stock. They pop up on ebay occasionally.

As far as the original seller, there was another deadworld mod kit prior to pinbits. I had one in a machine and it allowed coin operation and the latest rom where pinbits is only free play and the early rom. You may have a hard time sourcing the original kit.

http://www.iobium.com/judge_dredd_locking_ring_mod.htm

Forceflow's link includes the ROM it says and is not sold out.

https://www.pinbits.com/index.php?main_page=product_info&products_id=8

Enjoy a very fun game this is getting more popular as time goes on.

Just one more note ... the crane mod is another JD mod that is a must have and goes hand in hand with the locking mod.

http://www.pinballdecals.com/JD_CraneModUpgradePage.html

I wish I could find a blue ring for the locking mod myself (it has been sold out and not remade since) but I think I'm going to have to make it myself.