I am very satisfied with Hahnemuhle Ingres (German Ingres). Black. 95 gm/m2. I got it from Daniel Smith Art.
As part of the "mission" of The Light Farm, I'm always on the lookout for the materials we need that cross-purpose from other fields. If I have any say in the matter, handmade silver gelatin emulsions will be make'able forever, with little to fear from disappearing materials. Beyond the sensitizing chemistry for modern color films, silver nitrate seems to be the one and only real issue, and that even can be made from basic components (note: I am absolutely not recommending that for the amateur.)
But, back to the paper. I also have many hundreds of feet of the the paper used for film backing (got it from a film company in Hollywood.) Email me at firstname.lastname@example.org with your address and I'll send you a length of it to try. I think you'll enjoy making your own film. Very satisfyingingly cool.
p.s. One minor issue with diy roll film is that the backing paper isn't as lightproof at the edges as commercial rolled film. I recommend changing film in very subdued light. With the Hahnmuhle, make that very, very subdued light.