You could try emailing pics and some details to Rosebery Auctions in South Norwood. Or Bonhams do specialist poster auctions. They would tell you if they are worth consigning for sale, bearing in mind sellers premiums, and a rough valuation. If not worth selling, perhaps the Theatre Museum might be interested in a donation, rather than throw them away? Dealers usually keep an eagle eye on eBay, so I would think they're probably not worth much, I'm afraid.