how to get rust out of a scabbard ?

[kahnjar1]

DavidR's idea above is a good one but also perhaps a suitable size bottle brush would do the job if attached to an extension so it reaches all the way to the bottom of the scabbard. The bristles of these are usually plastic of some sort so should not do damage to the inside of the scabbard. Most hardware stores have these brushes in various sizes.
Stu