For Z mounts- Try this one made by Ultimak.
Aimpoint 10174 M-16, AR-15, AR-10, Forward Carry Handle Mount
Ultimak makes some very high quality AK rail systems and Im sure their AR parts are just as good. This one lets you use your iron sights as well even with the mount on.
For foregrips in no particular order...
Tango Down- Battlegrip
Knights Armament- Forward Pistol Grip
Troy Industries- Modular Combat Grip
LaRue Tactical- FUG -Forward Universal Grip
All of these lock on solid and or have an internal storage compartment for spare batteries/tools. Many of these models have a flat side for a tape switch too if you want. All of these brands are a bit more pricey but they are durable, battle proven and worth it.