Where should i farm weapons ?? I'm lvl 66 main a odachi and stuck in sekigahara i need to farm for gold and weapons but my damage output is terrible

If you can bump yourself to Level 70, I'd say go back to Onigashima and run Golden Weapon Hunt Youen on Hard, with a 300% drop boost of course (you can get ~70 golds a run there, and only gold ??? weapons drop). The weapons you get from there are pretty OP, and will see you through to around Echigo/Edo area. Youen's a real bitch of a dungeon though, so watch out for that. The Youen Hard weapons are from around Nakasendo, I think, which is either end of Kaga or just after it. Not entirely sure. At any rate, the Oadachi you'll get there will be around 2-3 times stronger than anything you find in Seki, and that's pre-enhancement.

Aside from that, you can increase damage output by using Oodachi Skill Force/Affinity magatamas. You should be focusing on boosting POW more or less exclusively, but have a little on MND as well so you can chain skills (only go to 40 MND max though).

It may also be worth checking the wiki weapon pages if you haven't already done so. e.g. http://onigiri.wikia.com/wiki/Odachi. The weapon links give the drop locations i.e. where to farm.