For air conditioning gas filling services in Istanbul, you can contact HVAC service companies or local technicians who specialize in air conditioner maintenance. Here are some options:

1. Armut.com: This platform allows you to find professionals for air conditioning services, including gas filling, in your area. You can compare quotes from different service providers.
2. Getir İşler: This app provides various home services, including air conditioner maintenance and gas refilling. You can book a professional through the app.
3. Authorized Service Centers: If you have a specific brand of air conditioner, such as Daikin, Bosch, or Mitsubishi, you can contact their authorized service centers in Istanbul for gas filling and maintenance.
4. Local HVAC Technicians: Many local technicians in Istanbul offer air conditioning services, including gas refilling. You can find them through local business directories or online platforms.
5. Kombi & Klima Servis: Specialized in both combi boiler and air conditioning services, they offer maintenance and gas refilling for air conditioning units.

Make sure to inquire about the type of refrigerant used (such as R410A, R32, etc.) as different models may require specific types of gas.