Some of the ones I know a little about have barrels that have the same outside diameter for both calibers -- I'm not sure that ALL of them are that way, but suspect they are. That might mean that a factory barrel will work and a conversion barrel is not needed.
Then, too, EFKFiredragon.com has a BUNCH of XD barrels, including conversion barrels. I've used a couple of their barrels and think they're top quality. (Customer service is first class, too.) https://efkfiredragon.com/springfield-xdsub-xds-xdt-xdm1.html
You or your friend might also check with Springfield, as a factory barrel (if it will work) might be less expensive.