Great Eastern Cutlery is the way to go, if you can swing the cost (you didn't mention a price limit). They're a rather new company, but they do things the old way, and they do them very well. For a medium-sized stockman, look at the #66 Calf Roper or #68 Buckaroo. The #92 Eureka Jack is at the top of my next-to-buy list. I mention these knives (even though I don't own one yet) because I have a personal bias towards mulit-blade traditionals with at least one curved and one straight blade. If that's not a priority for you, there's many GEC jacks that'll fit the bill, like the #15 Boy's Knife.
An alternative that I'd also whole-heartedly recommend would be to poke around eBay and pick up a '70's (or 1965-1969 if the cost isn't too outrageous) vintage Case. My personal favorites are the 6332 (precursor to the 63032) and the 6318HE. Both are stockmen that have a pen blade, which I much prefer, in place of the usual spay blade. The Cases won't be quite as "robust" feeling as the GECs due to the thinner blades and hollow grind, but they sure do slice nicely, and they're robust enough to handle anything that you'd want to throw at a non-locking traditional knife. And frankly, you just can't beat the the old Case red bone of the '60's and early '70's (IMHO).
Welcome to Bladeforums, the Traditional forum (perhaps the most pleasant, helpful, and generous forum on the entire internet), and the addiction. I hope your credit is good.