iPhone apps are “bundles” just like Mac OS X apps, but zipped. In OS X, you need to locate the desired app, which will have a .ipa extension (if you have them visible), then open it with the zip extractor of your choice. You will end with a folder. Inside this folder there will be another, called “Payload”, which contain the app (with a .app extension). Right-click to show the bundle content and somewhere in there you will find regular font files.
Captured from web.archive.org on 17 Apr 2015. view this capture
Marcellus also has a Pro version https://www.myfonts.com/fonts/stiggy-sands/marcellus-pro/
Don