You can make full round profiles on a shaper with a half round concave radius cutterhead that matches the diameter you want. It takes 2 passes. For accuracy, I prefer to use a sticking fence like the one shown. The first pass is made with square S4S stock run against the fence. For the second pass, a wood guide plate with a hollow groove to match the rod diameter is attached to the fence to align the parting line between the two half cuts. Once this is set up, it's pretty easy to run several hundred feet of stock through it. The photos show a lozenge shaper profile, not a full round; but the idea is the same. The outfeed hold down wheel has been moved back to show the cutterhead. This is a 2 knife safety head with shop ground hss cutters. You can buy 3 knife carbide tipped heads which are safer and easier to set up if you are not familiar with this type of equipment.
This is similar to the way dowels are made in high production on molders with top and bottom heads and milled bed plates behind the bottom spindle which cuts first. It won't hold the +_ 0.003" to 0.005" you can get on a molder, but you can come pretty close with practice.