Just a couple of suggestions, I design and make helmet visors. If you build a plywood mold box with a fiberglass face of the free blow area in your design, you can free form with vacuum, if you set up a solenoid valve and foot pedal switch you can "bleed" the box to control the depth of the bubble. Using Rit dye in hot water really works ! I did this about 20 years ago for a graduated tint, works great, and is permanent.
Alternatively, you can find bubbles on Aliexpress...see pic. The trim for the old Bell helmets is available at Pegasusautoracing.com. part # 4336-201.This is a project I want to tackle some day, I already have the vintage bell helmet they started with.