Destination blinds are becoming rarer these days - most operators use LED displays that are eay to update when routes change and don't tear like blinds do... Only London remains as a city where blinds are still the norm.
The main producer of blinds in the UK is McKenna Brothers - they use a material called tyvek. Tyvek is a papery material but considerably stronger. As well as being used by McKennas it is also used in the building trade as a roof liner before tiles go on. Tyvek is also used for envelopes and industrial clothing e.g. paint sprayers overalls. However I have doubts about its ability to stand the test of time as older tyvek blinds I own have become brittle and unwinding them risks them falling to pieces in the same way that burnt paper does. London Transport did, up until the late 1980s, make their own (and some for a few independent operators). LT blinds are easy to spot. They were made by screenprinting the destination, etc onto a paper panel. These was then stuck onto a roll of linen.(see image of route 720 blind) The telltale 'creases' between panels shows which blinds are original LT manufacture. I believe no other manufacturer used this method. Others used linen and PVC film. Sadly, the trend at the moment seems to be for people to cut them up into lengths and frame them. A few panels in an arty frame are offered for as much as £250. I have my doubts as to whether they ever sell though! There seems no rhyme nor reason for blind era/area popularity. The best blinds in my opinion were made by King & Flack... They made a lot of Country area blinds after LT lost green routes to the NBC. They used LT Johnston type and made them from a very hard wearing linen. Sadly the company folded some years ago. They were distinctive in that their Green Line blinds used little dots between the via points and some RML/AN destination blinds had qualifying points e.g. HIGH STREET or RED LION in upper/lower case and on one line.
In the past few years the LT destination blinds that have the tube lines in their respective colours to support Railway Replacement Services have gone for £200. Bristol is another popular area, as is Dorset. Number blinds are less popular. Every so often a tram or trolleybus blind will surface - these prove very sought after by preservationists. In general, if you are looking to build a collection, decide on which area you are going to concentrate on and set yourself a budget - be it per blind or for your entire collection. Trolleybus blinds are still very collectable and London ones, when they come up, are snapped up for big bucks!
Bear in mind that they are bulky and you may need to store them in a garage or shed - if so, be sure to protect them from heat, light and damp - oh yes - and moths and mice! I have been fortunate enough to get some winding gear over the years that allows me to display some blinds. A friend used to visit breakers yards and had a Routemaster front box which he sold to me. It includes the glazed front as well as the hinged board that held the blind winding gear. I also own an RF front box. If you are interested in blinds, I am in the process of writing an e-book on the subject. Please contact me if you are interested in buying a copy... Estimated print date: late 2013.