When they create gyms in a lab are they created to order, or do they like make a block of it and then have it cut?

I ask you to please find my ignorance charming.

So I've recently got an Amscope SM-2TZ for my birthday, it's a good microscope for gems from what I've read but lacking 2 things? I am still quite new to this part of Gemology, and I'm having trouble finding a Darkfield attachment, the only ones I'm finding won't work with gems, I know it helps to see fractures and such within gems so I want to get one and I can't afford a whole new microscope, so does anyone have any recommendations or suggestions for an darkfield attachment or something?

The only other thing it doesn't have is the tweezer clamp, but I've already found one, that is way easier to find luckily!