Having trawled through Google's archives it seems that such things were available from places like B&Q and Homebase years ago and are still available in the US (Amazon sell a kit made by 3M) but I couldn't find any reference to anyone selling this stuff now with the exception of DIY Plastics who are rather expensive.
I did have a stack of the damn stuff a few years ago - it was going for about a quid a pack in one of the local cheap shops... think I got rid of it all though :-/
Sorry, don't know if it's still available. However, a piece I put up 19 years ago (Sellotape brand IIRC) on the pane of glass over the front door is still there and in perfect condition. It is completely invisible unless you know it's there. It is held in place with double sided Sellotape, and was then shrunk with a hairdrier to pull it tight and remove any ripples. I took the effort to very thoroughly clean the window and surrounding paintwork before fitting it, including cleaning the area the double sided tape sticks to with white spirit. This care seems to have paid off far more than I ever imagined.
Meanwhile all the rest of the properly double glazed windows in the house had to be replaced a few years ago.
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