[HowTheyDoThat] Carved stone

I am looking for a stone, most probably a cabochon cut with a flat
top that can be top center drilled to take a small gold carving, has
a Mediterreanean blue color, will be octagonal in shape, and then set
in a signet (or “class”) ring. I think that agate would be the best
stone to dye and cut to get the shape and color. Does anyone know
who does this sort of work - a good lapidary?? Thank you in advance
for the help. Alexis