I presume you mean'cock beading' - a slim strip of wood, square on one edge, rounded on the other.
Most beading planes are side beads, designed to cut a bead and a quirk beside it. For this job, you don't need the quirk, so your options are wider. If you start with a square edged strip of wood the right size, your options include:
You could use the curved part of a small side bead.
You could use a small hollow, maybe a no 1 or 2.
You could use a small flat plane - such as a block plane - to knock the corners off and round them over.
You could use sandpaper.
You could use a scratch stock.
Or, if you prefer, you could use a side bead on the edge of a bigger piece of wood and then rip it off by sawing down the quirk. If you don't have a wooden beading plane, you could use the smallest beading cutter in a multiplane such as the Record 050 or 405 or Stanley 50 or 45.