The ASA Prepware app (for iOS) will give you the option of studying for 'Instrument for Foreign Pilots'. Although the database is not as comprehensive as Gleim or Sheppard, it is good enough for a pass.
While you won't be able to learn the questions, the content accurately covers the type of questions included. So for someone already with the required knowledge level, the test should be trivial.
If you prefer paper, I'll second the recommendation for Gleim, although I’ve also used the ASA in the past it wasn't as current or detailed. Sheppard is undoubtedly tops, if you just want the question bank.
Good luck.