Try here: http://www.archpro.com/column.html This is part of Outwater plastics www.outwater.com and they are great to deal with and usually very cheap. They have wood fiberglass and aluminum. I have never seen foam, I wouldn't think they would hold up. If you use wood then vent top and bottom correctly. If you use a split column to cover a post then be sure to use an approved method for joining the halfs or the crack will come through your filler, just like if you didn't tape a drywall joint.