I can answer #1... No. There is currently no production threaded barrel for a .40 caliber XD that I have been able to find thus far. Most gunsmiths that are worth anything (read: have real experience with metalsmithing, arent just tinkerers) should be able to thread an existing barrel, providing that they should probably also build the silencer for you as well.
Another solution is to purchase a tactical barrel, install it in your service handgun, then work with a smith to build a silencer that slips over the barrel and then locks onto the tactical Rail for security and stability.
LEGAL NOTE: CONSULT LOCAL AND BATF regulations on this subject before engaging in any of the above. This may not be legal in your area and if you do not have the appropriate registration/tax stamp.
Another solution is to purchase a tactical barrel, install it in your service handgun, then work with a smith to build a silencer that slips over the barrel and then locks onto the tactical Rail for security and stability.
LEGAL NOTE: CONSULT LOCAL AND BATF regulations on this subject before engaging in any of the above. This may not be legal in your area and if you do not have the appropriate registration/tax stamp.