bespoke pen blanks

Hi everyone, I know that this question has probably been asked many times, and I have looked at a few older posts on the topic, but I'd like to ask again if that is ok. I purchased a handful of pen blanks, not realizing they were too short for bespoke fountain pens. But I had planned to just...

I have a few kitless pen blanks made with alumilite clear slow resin cast in a bespoke mold from ptownsubbie. They range from translucent to transparent with swirls. These are excellent demonstrator fountain pens, asking $15 each plus priority shipping. If you're interested in more pictures...

Where does one find clear tubes for casting pens blanks? I have been using Ptown subbie silicone molds and pvc, but I have seen clear tubes on some videos.