I picked up glass discs that worked well for a stage insert for a cycloptic--I think they were meant to be coasters. I only used one of the four (on a microscope I no longer own), and I bet I have the others around. If you shoot me a pm with your general location, maybe you are close enough to pick them up (for free). My recollection is that I bought them on ebay, but I will have to check. Glass discs of the right diameter and thickness are not all that hard to find or expensive.

I have a stereo microscope illumination system with two goosenecks and a ring light. I bought it on aliexpress for not too much money and the quality is shockingly good. I wouldn't necessarily worry about the quality of the AmScope product unless your standards are very high. For most of my time with these microscopes I used super cheap ring lights that were actually intended for use on car headlights, along with a 3d-printed adapter. Worked fine.