For a blade small enough to truly *FIT* in a pocket, I recommend you look among the neck knife models available, since their M.O. requires relatively thin profiles and small enough dimensions to be unobtrusive. Otherwise, there are a few pocket-specific fixed blades out there. Beyond that, pick your favorite folder..... Or get a BIG pocket.
Among the Busse/Swamp Rat stable, check out the Assault Shaker from Busse or the Rat Shaker from Swamp Rat. They are only available on the secondary market, but do show up in the For Sale forum occasionally. You'll want to replace their kydex sheath with some leather pants, rough side out for pocket carry. Adding a lanyard fob is another add-on that I've found handy.
If you aren't shy about customs, a few folks whose very small blades I've noticed in the past are Virginia Custom Cutlery's Stinger model necker, Bill Siegle skeleton neck knives, David Winston, Gene Ingram, Ivan Campos, J Nielson, Jens Anso, Kathleen Tomey, Robert Hankins' Spare Change model, or RW Clark's Woodsprite model. My apologies to the many other custom maker's whose small blades have slipped my mind at the moment.
From AG Russell's offerings the Hunter's Scalpel, Woods Walker, Bird & Trout, or possibly Deer Hunter models might be able to take care of your pocket knife requirements.