Thank you both. The A 1 spares are £24.99 a pair but are a different size, so I think it would be wiser to spend a bit more and buy a new unit if I can't replace the missing parts. I've been looking for a used magnet for sale on PW for a while (which was plan A) and I've now moved on to plan B which is to try and replace the missing arms as the rest of the unit works perfectly. Fortunately, there's no hurry so I'm hoping to avoid Plan C, which is to replace everything. Having used the A 1 store before, I'd happily buy from them again if Plan B fails.