I have a metal support post that I wish to use to replace an old cedar post under a floor joist in my basement. I have the post (which has a heavy, threaded rod in the end to adjust to fit the correct height), but I cannot find a dimpled metal plate for it to rest against at its top end where it would actually support the floor joist. . These are not available at Home Depot or any hardware store in town. Where do you go to buy these things?