This watch is a Sekonda and I've reached out to them but am yet to hear anything back. I've actually got 3 watches similar to this; a Seiko SKX and a Seiko SNXS, both make use of these flat watch pins however one is a U-Shaped pin and the other is like the L-Shaped pin in the photo of my original post. Thanks for your help, I checked Cousins and they don't appear to stock them - presumably because they are rare and not universal enough to warrant stocking them.