The exotic weapons Kama (Double/Chained) and Kusarigama use larger dice than a d4. The Kama uses a d6 for both elements while the Kusarigama uses a d6 and then a d3.
Honestly the damage dice doesn't matter all that much since an increase from a d4 to a d6 is just 1 average damage.
and what feat would i have to use to be able to use Martial weapons with out a negative?
Martial Weapon Proficiency in that particular weapon. If you want proficiency in all martial weapons you'll have to dip a level of fighter or something. But you won't be able to flurry with them either way.