Here's one to start with. Hope it's useful.http://gmatclub.com/forum/gmat-prep-problem-collections-114358.html?hilit=gmat%20prep#p1017408
May be you can change the way you enter 'key-words' whilst searching to get better results.
For e.g. 'GMATprep' and 'GMAT prep' aren't the same - so there's a possibility you might get different results on these two searches. (Time is all you need
Hope this tip is useful for your next search
Giving +1 kudos is a better way of saying Thank You