I recently read a question somewhere in the e-world about eventual sellers of finely grained dremel drums. Cannot recall (or find) where,
neither say a word about sellers, but they can be made in minutes.
Wrap a full turn (or more) of double sided adhesive tape on a small dia. rod of suitable length. (and suitable dia., too! Don't ask why I know that).
Cut a strip of the desired grit sandpaper as large as the tape is.
Wrap the strip of sandpaper on it, cut it so You will have about 5mm overlap. Take care to wrap it accordingly with the supposed rotating direction.
Put a drop of glue on the overlap backside, wrap the whole into a strip of plain paper and keep it closed with some adhesive tape.
Let it cure for a while.
Make a few, while You're at it: they're not of the quick-replace type.
Marcello