there are some ideas for DIY on this site. Many of them could be painted black even tho that's not what's shown: https://scratchandstitch.com/30-diy-mirror-frames/

This looks interesting...I'd be cruising around lumber yards/hardware stores/craft supply stores (this comes from an auto customization/supply shop) looking for flexible materials, plastics, leather, etc that can be painted black. Look at plastic baseboard molding. This uses hose that could be painted black https://www.youtube.com/watch?v=Gxxpo_K7vqw

https://www.melanielissackinteriors.com/blog/2017/10/10/diy-large-brass-trim-circular-mirror

Look at this using dollar store toy snakes! https://www.domestically-speaking.com/diy-oval-mirror-frame/

https://thecollectedhouse.com/designer-dupe-diy-bauble-mirror/

"Is this something that can be DIY? What other suggestions do folks have on how I can achieve this?"

Yes; I've done it:

I'd use Nocturne Corian (solid black) with a high gloss finish if I were you.

Have you tried local frame shops? Maybe a local woodworking shop?

Love seeing Joseph's work. Nicely done!

For a simple black frame, you could cut your own wood circular fame and then paint it black. A 6ft diameter 1/4 inch thick piece of glass is probably quite heavy so you'll have to be careful about how you hang it to make certain it's safely supported.

"A 6ft diameter 1/4 inch thick piece of glass is probably quite heavy so you'll have to be careful about how you hang it to make certain it's safely supported."

Fortunately, solid surface is inconspicuously repaired.

Mirror mastic it to a custom plywood substrate, then apply flexible polyurethane molding around it, painted your color of choice. Mount with a metal french cleat /Z clip, secured to the studs.