Are there any manufacturers/suppliers of cold smoke brushes for bottoms of doors where the gap fluctuates from near flush to over 25mm across the width.  The building is very old with sloping floors, and the doors cannot be cut to size. 

If not, are there any other solutions members can suggest?

Thanks

A threshold gap of 25mm is excessive for both fire resistance performance and smoke spread performance. Can the floor condition be remediated and/or can a threshold plate be fitted to the floor directly under the door in its closed position?