For most subjects, past papers help you predict what might come up. Unseen poetry is different: you will never see the same poem twice, so past papers are not about content at all. They are the best way to practise the skill under real conditions, with genuine AQA poems, questions and mark schemes. Used properly, they are worth more than any amount of rereading.
Where to find them
The official source is the AQA website, which publishes past exam papers and mark schemes for English Literature Paper 2, including the unseen poetry section. Your teacher will also have access to these and to specimen papers. Work through as many as you can get hold of, because each one gives you a fresh poem to practise on and a mark scheme to check yourself against.
How to use them well
Do not just read past papers, sit them. Give yourself the real time limit, resist looking at the poem in advance, and write a full answer as if it were the exam. The whole challenge of unseen poetry is analysing well under time pressure, so practising slowly or with the mark scheme open defeats the point. Afterwards, mark your answer honestly against the scheme and note exactly what a higher answer would have added.
A note on the poems
The poems used in past papers are often still in copyright, so you will find them printed within the papers themselves rather than reproduced elsewhere. That is fine, because you do not need to keep or memorise them. Once you have used a past-paper poem for practice, its job is done; the skill you built on it is what you carry into the exam.
Prepare for past papers with the method and structure guide, check yourself against the mark scheme, and build the habit with the revision routine.