https://ugmonk.com/collections/accessories-1/products/small-analog-card-sleeves-set-of-6-earth-tones
Ugmonk selling index card dividers (as "analog card sleeves") as a set of 6 for $12. They're fun colors but don't actually have tabs. They also function more as sleeves or folders for notes, but it's not immediately obvious how many cards they'd hold.
https://launch.getthinkable.com/
Looks pretty, but in the end it won't be as highly functional as it looks pretty. I'd rather have a mahogany card index. Dollars to donuts this doesn't actually launch.
Reminiscent to Ugmonk's Analog System: https://ugmonk.com/collections/analog
Jeff Sheldon is the founder and designer of Ugmonk, a brand focused on creating high quality, well-designed products. What started as a small side project in 2008 to create and sell simple t-shirts has grown into a full-blown lifestyle brand which Jeff now runs full time.
https://www.nerosnotes.co.uk/collections/foglietto
Looks sort of similar to Ugmonk's offerings...