Are past tests available? How to prepare, using practice or real tests?

[CKgre]

Hi,

I wonder whether past tests (especially all tests after the shift from old to new GRE) are available in paper form?
I heard there are 4 real tests in the market, but is that all?
I think using the real test is the best, but if there are only 4, I'm afraid of consuming all of them before I'm ready to take full-timed test.
I'm thinking to read some prep books and then take the real tests...is this a good way to prepare for GRE?
Or should I only use practice tests (not real ones) and save real one for timed test?
In that case, which company's practice tests would be the best?

Thank you in advance.