FYI- You're talking about 2 different things here. Some of the names you mention manufacture AND turn (contour) the barrel, but others just take a barrel blank (cut rifling, but no outer shape yet) and contour it by spinning it in a lathe and cutting the outer dimensions to fit a certain application.
Douglas is a barrel maker, they actually bore the tube and cut the rifling and do some limited conturing. Compass Lake contours barrels from Douglas, Krieger, any barrel maker you might want. Noveske contours Pac-Nor barrels exclusively. White Oak is also a contourer, not a barrel maker.
Noveske Barrels, despite being called SPR, are not contoured to SPR specs. If you want the OPS Inc barrel collar, then you have to order that specifically from Noveske. John does know the true SPR spec, but it's a special order item.
Unfortunately, "SPR" barrels are easy to find, but you'll find these are more or less just stainless steel barrels cut to 18". They're high quality (usually), but they will are not SPR spec and will not fit the OPS Inc collar and might not fit your gas block if you have the "other" size. This might not matter to you, but just be aware of what you're ordering.
Wes would be a good guy to get it from, he knows the difference. Many do not.