To my knowledge the only source of beast master feats is Martial Power I, and there is no "Your beast gains a +2/3/4 feat bonus to damage" feat that I see. The only damage feat I can find is Coordinated Oppurtunist which is +2 dmg for YOU on oppurtunity attacks if target is adjacent to beast.
Tangent Alert: Looking through the beast master feats I can really see some flaws in the "every race-class combo gets a feat" theory Martial Power tried to implement. The feats aren't (all) bad, but they're so specific and numerous it makes finding anything generally useful a pain in the attention span.
Truthfully, the Beast Master build is NOT at all underpowered in a basic sense. The only issue it has is the lack of access to a certain set of highly potent feats. Beyond that, the lack of the TWF's larger off-hand weapon is trivial (.5 point of damage on a hit, not a big deal). The only other lack being access to a truly world-shaking PP like Battlefield Archer.
So, you don't REALLY need to fiddle with their powers, they just need maybe 3 really nice sky blue feats and a sky blue PP. There is a misconception that, because the beast is not a combat monster, that the build is 'bad in combat', it isn't. It is basically just as effective as the other 3 ranger builds, except without some fairly small extra benny. In return you get a basically unkillable companion that can take hits for you, do OAs, set of traps while you are nice and safe at the other side of the room, carry stuff, etc. (heck, if you're a halfling there are beasts you can RIDE, beat that!). Heck, I guess a pixie ranger could ride ANY companion, hahaha.
Anyway, I have nothing against some powers that push the beast more into being an ersatz weapon, that isn't a bad idea at all, but it should be thought of more as 'color' and not so much as something needed to 'beef up' the build in any way. [MENTION=82504]Garthanos[/MENTION], the +1 hit and damage bonus you are giving is OK, it certainly won't break anything and isn't going to make the character stronger than an optimized twin striking build. I wouldn't go any further than that, except maybe to extend it to some non-at-will versions.