Well, I just bought a beautiful one on ebay that I am going to have to resell because it is snug. I'm so disappointed. But I think that the sleeves will be too short for you--we are the same height and they are a bit short for me.
It doesn't HAVE to be a melton! Just wear any black show coat even! Just buy/wear one big enough to wear some layers underneath; much cheaper maybe? NO one will be checking to see what material your coat is or what weight it is....just any nice black riding jacket would do!
I second that it's proper for grooms to wear ratcatcher too btw.
I'm bumping up this old thread because I am looking for the same... though I'm not desperate yet. Any good resources for this in or near Colorado? Or is my only option to get something sight unseen?
IDK about Colorado but Middleburg Tack Exchange would be my first go-to. They aren't close to me either but I've called them a bunch of times and had stuff shipped. middleburgtack.com Always had a good experience with them. Good luck!