Back in 1976 when IPC were forced to suspend Action weekly because of its violent and anti-authoritarian content there was one issue that was never distributed. Only 30 issues of the issue dated 23rd October are thought to exist now and one in great condition is currently on eBay!The bidding ends on 31st May and at time of writing (23rd May) the bids have already reached £521. Far too high for my pocket but it'll be interesting to see how much it finally goes for.
If you want to bid, or just follow the auction, go to the phil-comics page by clicking here.
My thanks to Hibernia Comics for bringing this to my attention. Images taken from phil-comics' eBay page.
UPDATE 26/5/2015: On his Down the Tubes blog, John Freeman has dug a bit deeper on the background to this story and found that a full print run of this issue was printed, but the large majority were pulped. See here for the details:
UPDATE 31/5/2015: The winning bid was a staggering £2,555.00. Blimey!