I’m interested in plastic alto at 415Hz, too.
Recently, I started consider 3D printing as valuable way. I don’t have access to a 3D printer but there is a service in my town that can print almost everything with an huge variety of materials. This service printed for me a spare body tuned at 415Hz for my 440Hz Yamaha alto recorder.
I started from here: https://www.thingiverse.com/thing:712940. As you can read, this model is a copy of this instrument: http://www.bergstrom.dk/draw01.pdf.
I just modified that model in order to fit in Yamaha’s head and foot and get the right lenght, measuring distance from labium to first hole.
The sound is not bad, very similar to Yamaha’s one. It costs me 35 euros due to the drawing work but now I’ve an alto at 415Hz.
If you are interested, you can contact the print service here: https://www.fabbrica3d.com