There are only 2 compatible controllers, I believe, and theyre listed on his blog. Today, I bought the Moga Ace and it works very well, however is fairly clunky.
There's a logitech version that actually has a very sleek design and has an extended battery as well.
If you have an iPhone 5, 5s or SE, you could try this one: https://www.amazon.com/Logitech-PowerShell-Controller-Battery-Generation/dp/B00FHREO8K.
I worked for me on my 5S. The only problem was the physical connection that sometimes would not connect properly to the lightning port. It doesn't use bluetooth. I also didn't like the analog control.