Always glad to see the experienced craftsmen on here offer not just the big ticket items and services, but also the various odds and ends we may need, like bubble lenses, at a reasonable price.
I'm updating my Don Post Classic Action Darth Vader helmet and wanted to try my hand at making my own replacement bubble lenses.
I found this product I bought from amazon.com for around $10 was a good material. Be sure to get TRANSPARENT not translucent.
Smoked Tinted Transparent Cast Acrylic Sheet 12" x 12" x 0.118" (1/8") Gray
Brand Name AbleDIY
Part Number Gray #2064
UPC 723175404557
It's thicker than the typical bubble lens material, and more heat is needed for it to become workable and trimmable (around 225°F). But I found it stood up to several reshaping iterations without much distortion.
You'll also need a heat gun, gloves, and (preferably curved) lexan or other snipping scissors. I used a sculpting wire to capture the outline of the inside of both eye sockets to shape a single visor to cover both eyes.
I pulled the heated plastic over the short coffee mug shown to provide the bubble shape (worked better than a tablespoon I'd first tried!). It's not a perfect flush fit, and I know there are better ways to make it so, but it's good enough for this DIY project and looks fine to me.
The tint will not look very dark with backlighting, but once the helmet is worn or the dome is attached, it has the appropriate darkness and good reflectivity.