The GPS source in FLARM does not have any aviation certification. However, you can use a non-certified GPS source in most countries in aircraft with MTOM <= 5.700 kg. The transponder/ADS-B Out equipment must then be programmed with the required integrity setting and other parameters. Contact your maintenance organization for details.
Also note that the GPS used in FLARM has much higher accuracy and precision than aviation certified GPS sensors. Aviation certification of GPS is focused on integrity and error reporting, not accuracy (the purpose is separation and navigation, where the required accuracy is in the order of magnitude of hundreds of meters or several nautical miles). Most aviation certified GPS sources do not have the required accuracy and precision for VFR collision avoidance purposes.