Push the “Add to Game” button under “Buy” and you can add it to your game and buy it from the game’s page.
Example (you can see the Buy buttons there):
A bit off-topic, but do you know if iOS items can be bought on Android, and they’re really just mobile items, or are they true iOS-exclusive items?
I tried buying these while using BlueStacks tablet emulator (not iOS) and it wouldn’t let me buy those.