Here's a site where I've ordered many stands:
https://www.displaystands4you.com/
I'm not sure if they make custom stands, but I've found that almost everything I want to display can be done with one of two styles, depending on the thickness of the page block:
cs12 Large Textbook Easel (books up to 2.6" thick) and
cs5 Wide Book Holder w/o Lip (books up to 1.4" thick).
I've also had some worries about the 90-degree bend being slightly curved, and not perfectly straight, so to prevent spine cocking from the back board being ever-so-slightly-higher than the front board, I've affixed some felt pads to the area where the back of the book touches the stand. This keeps the bottom of the boards both touching the acrylic. (I admit, this may be a manufactured worry. I've also accepted the fact that my books bring me the most joy when I can see them regularly, and if displaying some of them causes minor issues over the long run, it's worth it to me. Obviously I still try very hard to stop any issues from occurring at all!)
One thing I have
not tried, and should, is using a plastic block to hold the page block in place, as recommended by RF. Granted, I haven't tried displaying any
Stand-sized books (anything thicker than ~2.5"), but I'm definitely going to look into this...