When I taught IB French B, we used a couple of A Level books and pretty much wrote our SoW around the A Level topics. For writing tasks, we wrote our own essay titles and incorporated those into our teaching. I also used past IB papers and made a list of essay titles, and we practised reading questions from there too. I found that there was more flexibility and freedom teaching the IB and I loved it. Your new school will send you on an IB course as you start teaching it, or at the end of your first year of teaching. I got my (then) job without any IB experience. I was told that as long as I could teach A Level (which I was already doing), then IB wouldn't be a problem.