What if I run out of study materials?

So I will give my test in April which means i still have time to practice a lot

I already practiced cambridge books 11-14 but I'm afraid I'll run out of materials after I finish 15-18

Do you guys know other authentic materials? I heard the ones available online aren't reliable

Should I repeat the Cambridge tests again or is that counterproductive?

I also heard about ielts ready premium if I registered through the British council Should i try that? are they as good as the cambridge books?

Thanks in advance to anyone who replies