Oh shoot, I should have noticed you are on iPad. You'd want to check for iOS compatible devices, it looks like some of them require you to use a desktop PC to set them up first. I think it would basically act like a keyboard so you would want to look up what the keyboard shortcut would be on iOS.

If you go to Amazon or similar and search "macro pads" you should find devices similar to what you want with different numbers of buttons. I don't own any so I can't give specific advice but if it says programmable you can set each button to run a key combination (ie shift+F3).