Eorzeapedia says there is one for Rank 10 Marauder in Limsa Lominsa: NPC is Kerrich at coordinates (7-6). It costs 43,200 gil. For the most part, you are intended to make your own weapons (or accumulate the materials and have someone else craft it). The NPC costs are likely highly marked up from what you could manage by getting the parts yourself.
Edited, Sep 29th 2010 4:57pm by Kaelia88