Have you checked out the Advanced Race Guide? It has alternate racial traits for half-elves that allow them to express their drow heritage. As for drow orc, do you mean half drow, half orc, or a version of the orc that lives in the darklands and is similar to the drow? If the former, you'd probably need to create a new race using the racebuilding rules in the back of the ARG; if the latter, I don't really see anything making the orcs as they are unsuitable for life in the darklands -- they already have darkvision and are chaotic evil. Just have them be darker-skinned orcs and that's about it.
If you want a Drow/Orc hybrid you can use my Elf/Orc hybrid and modify it with the alternate racial traits and feats for half-elves.
-0 Humanoid (elf, orc)
-0 Normal movement speed
-0 Language Standard Array, starts with Common and Elven or Orc
-2 Flexible modifiers (+2 Str, +2 Dex)
-2 Orc Ferocity
-2 Elven Immunities
-2 Skill bonus (Perception)
-1 Low-light vision
-2 Darkvision 60 ft.
=11 RP
The main problem of that race is that they probably have better chances of being killed right after birth than tieflings and dhampirs combined.