Loose your tube, bugger it up, damage the threads or simply have all the other parts to make up a complete Kit and just need a tube? Here they are. Factory New Remington 12ga Extension tube is various finishes. These retail for $29.51 from Remington except for the nickel coated Marine which is $51 on Remington's Web site.
If you are putting one on a 20" Express barrel select the Three Shot Parkerized as the Black Oxide Finish of the Express is designed to look like Parkerizing so you will have matched the finish. It will extend 1/2" past the barrel.
Use the drop down box to select the tube you want. Your are only getting the tube with this purchase not the entire kit. There are other parts in this same category if you are missing other parts.