Any 24" (60cm) industrial, high velocity or drum fan will be of similar performance. Drum type fans are usually a little higher performance than open cage style, so you might be able to go one size smaller 20" (50cm) with a drum type. A quick search on amazon.co.uk for “industrial fan” turned numerous hits. Larger fans will move more are at lower RPM resulting in quieter operation…but, they cost more. I wouldn’t go smaller than a 50cm Drum or 60cm open frame.