Airsoftjunkiez just had a huge restock of HPA triggers from SPEED Airsoft. These are the tunable M4 flat triggers  designed to work with Polarstar and Wolervine HPA conversion systems.

Sureshotmidget14 does a speed test on the 3D Printed Triggers from TAPP Airsoft. TAPP Airsoft sells online different types of 3D-Printed triggers such as the Scyhe, Blade, Cutface made for Version 2 gearboxes or the Valken V12. These can be ordered via the Sculpteo online store.

Straight Sigma Triggers from Prometheus for M4 AEGs are available at Airsoft Atlanta now... "The new Prometheus Straight Sigma Trigger made for standard M4 AEG airsoft guns. Red, Gold, Silver, and Black colors available. The straight trigger that matches stylish hand guards and frames, sharp design.

Another release from SPEED Airsoft aimed at those who are looking into tunable M4 triggers for their HPA-powered AR airsoft rifles... "SPEED Airsoft new Externally Tunable HPA M4 Triggers will bring out the beast in the Polarstar and Wolverine HPA conversion systems.