Yesterday I made my most recent pen with a funny (not really) tube size so I made two neat fit bushes on my metal lathe,if you do not have this backup you can still make your own on your wood lathe, especially if its seldom used sizing. Indeed to enable complete finishing and using CA etc for finishing I cut back the shoulders of bushes to allow turning at the ends without catching the bushes on the chisels, or worse glueing them to the blank. Let your Calipers be your best friend or turn between centres and eliminate the need.
Peter.