I recently purchased a mulching kit (Honda part # 06725-VA3-S00) from boats.net for $14.72. This was for my HR215K1 mower. The kit contains the upper mulching blade, a spacer, 2-10x25mm blade bolts, and 2-spring washers. The instructions that came with the kit show that you are supposed to utilize the original cutting blade with the new upper blade from the kit (I also bought a new original cutting blade so both blades would be new), and also show how all the parts fit together. The 2 new bolts are required because with adding a 2nd blade, the original blade mounting bolts aren't long enough. The instructions also indicate that the kit can be used on the HR214.
This kit is only shown as available for model HR215K1 at the boats.net site, so enter this model designation to find the kit. I also have an HR214, which currently in out of service, but I will eventually be buying another of these kits for the HR214 when I get it running again. The HR214 and HR215 use the same original cutting (non mulching) blade, so it looks to me (by comparing the kit with my HR214) like the kit will also fit my HR214. I have cut my lawn both with the non-mulching original blade and with the mulching kit installed. The mulching kit cuts the grass into very small pieces compared with the regular blade, and if you choose to bag with the mulching blades installed, the bag will hold more grass because the cut grass fits more densely into the bag. The mulching plug isn't available from Honda anymore. I do have the plug, but tried mulching (not bagging) w/o it one time and it seemed to work ok, but the rear spring loaded door kept opening a little bit with all the pressure inside the deck and some grass leaked out, so if I try that again I'll rig up something to keep this door tightly closed.