We bought ours on amazon! We actually ordered a bunch and he picked his favorite one (free return shipping on most of the ones we found). They're very affordable ($20+) and is the exact same material (if you are going for tungsten) as the ones you'll see in jewelry shops that cost 10x as much.
This is the one we ended up with: King Will Loop Tungsten Carbide Wedding Band 8mm Rose Gold Line Ring Black and Silver Brushed Comfort Fit5 https://www.amazon.com/dp/B07CWNY6X7/ref=cm_sw_r_cp_apa_tNITBbSQ4ZWEH
We're not married yet- and he has expressed hesitation about wearing a ring everyday- but he's actually excited to get to wear this one! It's also pretty unique and can be worn in formal and informal situations. The same seller has tons of options.