Call Dan Wesson and ask them where they got the original ones. Obviously they have some supplier for them.
My understanding is each caliber of the revolver series has a different thread and pitch so you cannot accidently screw a 22 lr barrel from a 722 into a 357 mag md15-2 frame. I honestly have never tried it on my guns, but eyeballing it they did look different to me.
Do you have an old 15-2 or a new one? Mine is an early Palmer 15-2 and my new one is a 722 from the current DW. Both are really good revolvers let me add.
Because I purchased a new 2.5 inch barrel that had a tiny burr on the threads...
I hand tightened it to where I noticed it getting tight when I first opened it. Upon pulling it out I saw the tiny burrs. They were small so I thought running the small nut over them would clean them up enough to get the new barrel in. Didn't help. Then I went to put the 8 inch barrel back in and it no longer wanted to go in past 1/4 " into the gun. I'm amazed that the tiny little burr and hand tightening could damage the internal threads enough to need to be retapped. The 8 inch barrel still shows no damage to it's threads. I thought I posted on here earlier but it's not here now. I'm hoping to either find the right tap and die set or make arrangements to send my entire gun in to get it back to where it was.