This topic has been covered a number of times and a quick site search from the home page turns up a lot of replies. However, I remember Michael Gilligan replying in one thread saying that he bought a packet of them from an eBay seller and giving a link, as a result of which I did the same and got a packet of 50 for about £3 inc postage from – guess where? I can't find the thread now and anyway the link will be long out of date I would imagine, but you could try a search on said site.
John
P.S. just looked on eBay and they're all over it but the price has gone up to circa £5 for 50. Cheaper if you only want a few.
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Edited By John Hinkley on 28/08/2023 12:54:00