OCR H240 Maths Practice PapersWatch
I will try to find the ones I have. Perhaps you can find them useful but I wouldn't get my hopes high. I recommend doing papers from AQA, Edexcel, Wjec etc as well because they have similar questions and there won't be much difference in the questions.
I second the advice given and say that on the pure side of the course, the exam boards are pretty similar. Imo, if you want a challenging paper, AQA 7357 Paper 1 June 2018 is an excellent paper to have a go at, partly as it's a live paper, and partly because it's pretty damned hard.
Anyway, if you're looking for challenging applied Papers (which have been released!), Edexcel produced a nice set for June 2018 (ignore Q1 since it's on their LDS).
I'd say they're well worth looking at. Especially Paper 1. Apologies for the major confusion earlier.