Don't know anything made specifically for the job, but if you're after something non-permanent, but which might hold better than a plaing plug...how about an old schook bar end plug, Milremo or such. They work over a fairly tight diameter range, maybe 20-23mm ish.:
Otherwise, I'd vote for a starnut or to cap expander. What's the internal diameter?
Re star nuts, I would avoid them as they can twist in the tube and can be a pain to fit anyway.
The BBB style expander just slip in, you tighten the bolt and then you have an easily removable solid fixing.
Assuming the expander fits of course and the top sleeve on that style will sit in the tube.
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