Steve Grattan inquired about a source for Wurlitzer Duplex Frame
roll cores (2018.03.02 MMDigest).  If he truly seeks the cores only,
I would imagine that typical Schedule 40 PVC plumbing pipe with an
I.D. of 2" and wall thickness of about 3/16", cut to desired length,
should serve adequately.  Adapting the core to an axle & flange
should be relatively straight-forward.

John Grant