Have you looked at Jewels by grace? I think she has a few that might fit your criteria. Old world diamonds as well.
A classically beautiful diamond solitaire featuring this chunker of an old mine cut! There’s nothing we love more than old cuts here at JbyG, and we think that this stone makes quite the gorgeous engagement ring. Set in a yellow gold 8-prong solitaire, we wanted to emphasize the natural shape of...www.jewelsbygrace.com
You might try Ivy and Rose. This is bigger than you’re looking for but they may have something else a little smaller:
This absolutely breathtaking 3.80 carat old mine cut diamond is dazzling in size and has gorgeous, fiery brilliance! Certified by GIA, the diamond is exceptionally clean with VS2 clarity. The diamond has a truly phenomenal presence, full of bright, lively sparkle, vividly colorful fire, and antiquewww.etsy.com