FN sells the 10" and 14" barrels. Or you can go the route of having it cut down. The latter option is cheaper for sure. I just got the factory barrel installed yesterday...very nice. I've also seen some nicely cut barrels...especially the ones done by Marvin Pitts.
Both are viable options in my opinion. Search the forum and I believe it's been argued back and forth to death. There's a chance of the chrome lining flaking if the barrel is chopped, but the stories I've heard compared to the amount of people that have done it means it's rare. A lot of people go the chopped way since it saves a good amount of money. Considering you spent $2k+ on the weapon, $200 on the tax stamp and god knows what on the accessories, I wouldn't make that my sole reason to pick the less expensive option.
Marvin @ Nefarious Arms and another who I won't even name are known to do the work. A lot of people have recommended Marvin @ Nefarious, although sometimes his communication turnaround can be something of an annoyance.
Personally i had mine cut down because I wanted 10.5" instead of the 10".