I am posting this to make the 3D printed bell and mouthpiece available to anyone who wants to build a P-bone (PVC trombone). We used the plans posted by others using o-rings inside the tubes. I am not including the design files for the the main trombone since other people have already posted great designs for this.
I used Creo Parametric to create a bell and mouthpiece. I tried a few different sizes for the mouthpiece and got feedback from student trombone players to see what they liked best. The mouthpiece and bell work well. The bell is is thin to get it to be light and resonate well, but it won't hold up well to being dropped. I have posted a bell and mouthpiece stl file. I also tried a few other shapes. I have also added prt files from Creo Parametric if anyone wants to modify the design. I do have other versions of these files available if anyone is interested.