Summit Machine may have the M24-15 weld-in inserts, call Mike.
I know they have the tap because they use it for their alum WJ tierod....which could be an option as well, not sure of the length compared to the XJ application.
http://www.summitmachine.com/index.php?p=customParts
M24-1.5 is right. Nobody has carries a weld in bung, unless you custom order it maybe? the RH tap can be found with some searching, the LH one gets tricky to find. i researched both options heavily, but ended up just gettin the JKS tubes already tapped when i did my wj swap.
With that said, and what others have stated..I'm not after the taps, looking for tube inserts. As far as I can tell, anyone who makes parts for these just threads the rod directly.