I hope my comments are not inappropriate. If they are not in compliance with forum rules, the moderators may delete them.
Anyway, I would recommend that you check the Contemporary Longrifle Association (CLA) artisan's website. Several brain-tanners market their products there. I bought a smoked braintan deerskin from a fellow named Bender in Pennsylvania. This particular hide did not "break down" as soft as he liked, so he gave me a very good discount on it. However, it was perfect for my needs. Firm, with no "drape," yet nowhere near as stiff as rawhide, and the smoke gave it a really nice color.
I don't think the forum rules allow me to post a link to classifieds in another forum. You may be able to find the CLA artisans' website with a Google search. If not, send me a PM and I'll help you find it. I also corresponded with Mr. Bender by email, and I may be able to recover his email address so you can communicate with him directly.
I believe a hide like that would work well for knife sheaths. That sheath you showed with your Woodbury-style knife was very well done. I would like to see you make some more of those.
Notchy Bob