We propose a novel method to search for possible new macroscale spin- and/or velocity-dependent forces (SVDFs) based on specially designed SmCo5 spin sources and a spin exchange relaxation-free (SERF) comagnetometer. A simulation shows that, by covering a SmCo5 permanent magnet with a layer of pure iron, a high net spin density source of about 1×1022/cm3 could be obtained. Taking advantages of the high spin density of this iron-shielded SmCo5 and the high sensitivity of the SERF, the proposed method could set up new limits of greater than 10 orders of magnitude more sensitive than those from previous experiments or proposals in exploring SVDFs in force ranges larger than 1 cm.