Aah, mine's AQA. I've never used Edexcel so I'm not sure how similar the specs are... if you can't find any past papers on the Edexcel website for B3 you could try another board and see how similar they are? For AQA B3/C3/P3 there's only the specimen paper and nothing else so I've tried some from other boards and just skipped the irrelevant questions... or you could ask you teacher sometime they're sometimes allowed the old past papers before they're put on the website :P