They'll fit in a regular mold with zero to minimal modification (carefully close and hit with rubber mallet, or a dremel). There are a bunch of options for round head no collar molds from Do It.
Warning : take the handles off the mold before you smack on it . Make sure it is on a flat very solid surface. Not metal unless it's a block of lead. The vibration can cause the handle to split if it's left on . Do one cavity at a time.