You have a few different options, all from the official test makers / with official questions.
They also publish two other books, one for Quant only and one for Verbal only. Each has 300 questions. You can take a look at their website, our website, or Amazon to see those titles.
Have you downloaded the free GMATPrep software yet? (
www.mba.com) If not, go download it. It contains 2 free practice tests and 90 free practice questions. You can also buy an add-on question pack of Q and V questions (about 200 each).
They also have a product called GMAT Focus (and I think this is their best product, out of everything they have). It consists of 24 quant questions but here's the cool thing: it's adaptive, just like the real test. No other materials are adaptive (except for full practice tests of course). So you can get test-like practice with timing / decision-making, since you can earn harder questions. When you're just doing random questions out of a book or question bank, the questions aren't adapting to you. If you think one of your issues is timing / decision-making on quant, then I highly recommend this one.
That's >1,000 additional questions across all...so that should keep you for a while.