The best way to let the brokers who don't support P5 for a product, is don't purchase it, but more importantly, let them know that you'd like to, if P5 mat files and such are provided with it. Give them incentive, and let them know you are interested in their work. Just "not buying" doesn't tell them if a product is just unpopular, or if it could be more so. Creating a set of P5 mat files in Mat Pose Edit takes just a few minutes, and at least shows an attempt at support. I do it all the time, going backwards from p5 to P4 mat files.. ;)

Way too many people take way too many things way too seriously.