May I ask why you specifically want a plastic reel? There are problems with many plastic reels. First off, most of them have slotted hubs which is not archivally acceptable. Ampex/Quantegy made the best plastic reel I know of, but I have no idea who, if anyone, has access to those molds. The reel in question had only one small threading hole per side. It was shown on page 82 of Magnetic Tape Recording for the Eighties (NASA Reference Publication 1075.)
Another problem is that the flanges on plastic reels tend to have large, multiple windows. This means less protection for the tape and more dropouts.
Before you purchase any plastic reel, you would be well advised to obtain a sample.
If, for whatever reason, you absolutely must have a plastic reel, here is a link to another source.
As always, the opinions expressed are my own and not those of my institution. Also, any mention of potential sources does not constitute an endorsement of said sources.
From: Association for Recorded Sound Discussion List [mailto:[log in to unmask]] On Behalf Of Martin Fisher
Sent: Monday, March 14, 2011 3:53 PM
To: [log in to unmask]
Subject: [ARSCLIST] Ten Inch Plastic Reels
Does anyone know where to obtain 10 1/2 Inch plastic reels for 1/4 inch tape???? No boxes needed.