No idea about the triangle bits left over :-(

Here's a diy build: Build Your Tools • View topic - DIY Stencil Cutting Drag Knife Solution - Update 5!

Rockcliff do a holder for $70 here: Rockcliff CNC Machine Inc.

Here's an article from the Rockcliff forum aparently Mach 3 has a tangential knife routine for motor driven blades that does all the lifting and dropping and turning: tangential knife cutting Styrene - CNC Machine Builders ROCKCLIFF Forum, Register it's free

Hope these help.