Just about back up to speed with my 40k stuff now, and hopefully I shall actually have some painted minatures to share soon. However, as I'm in the middle of moving house, I decided not to do anything too ambitious and though I might roll off another fluff document.
This is the chapter organisation chart for my Spears of Mawdryn Arthurian/Celtic Marine Chapter as it stands in the "present day." It only has three Companies, the rest being wiped in a bit of a massacre.... (is that an oxymoron?) Throughout its history, the Chapter has never really adhered to the Codex Astartes-prescribed organisation, and its companies have always been "Independent" - each containing their own Veterans, Support, Reserves etc., and as such able to deploy without awaiting for other elements of the Chapter to provide other required support or materiel.
Anyhoo, enough waffle, here's the chart. Some of the numbers, particularly where squads are concerned, are a little arbitrary at the moment. If you have any questions about the Chapter, fluff, pronunciation of Welsh/Brythonic names and terms.... just ask.