Firstly, we always recommend to purchase the Wifi+Cellular (4G/5G) iPad which has an inbuilt GPS. This works fine for most people. If you have any problems, or have a WiFi-only iPad, try one of the following:
The Bad ELF GPS Pro is a great device that allows multiple iPads to use a single receiver. Also doubles as a data logger.
The Dual Bluetooth GPS has also been reported as being very good by some customers.
Gamin GLO GPS+GLONASS device that works very well too.
This list isn’t comprehensive, and is based on customer feedback. Technically, any GPS that says it supports iOS should work with OzRunways.
Another option is an ADS-B IN Receiver that can also provide your iPad with a GPS position, so you get both ADS-B traffic on your maps and a GPS location for your iPad (2 in 1 device).
For example the SkyEcho 2 or Stratus 3 units shown here: ADS-B IN Receivers with GPS