Regardless of what resources you use, your study plan should involve a great deal of review.
Study question 1
Review question 1
Study question 2
Review question 2
Study question 3
Review question 3
Now go back to questions 1-2-3 -- and without looking at the answer, go through the thought process you wish you had originally done - and think through these 3 questions. Do you arrive at the right answer?
Keep going these batches of 3 through a set of 30 questions.
This way you build up mental stamina in small batches of 3 - and increasingly to more as you increase the batch size from 3 to 5 to 10.
Eventually, you will have to sit through an entire exam without rest - so building small pieces of stamina will add up over time.
As for questions themselves, you can find them at our Practice Pill Platform:
https://www.gmatpill.com/gmat-practice-test/