I personally do have good experiences with Dipl Ing Heydenreich, or 'Heylight'. He built me a great post for my Yo-Eddy. He can also build a 25.8mm one for you. It is maybe not the cheapest solution, but they are really nice engineered posts. Another positive is that they are period correct with early 90s bikes, as the post was already around back than.
Alternatively: BBB has their SkyScraper which is available in almost all diameters. Not so costly and a quite decent post. Only put a Retrobike sticker over the BBB decal
I am not familiar with new post, so these are the only two new offerings I know of. Back in the day you could also have post in that size from Syncros, Nitto, Kalloy among more, but I do not know whether that still is the case.
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