I believe that the only company to ever make a set of 9 Balls with no numbers on them were a German firm called Raschig. I've heard people say they were perhaps the best set of balls ever made for Pool. Making them without the numbers or stripes (
Which are a seperate pieces of white plastic in standard balls like Aramiths) should mean you can achieve higher tolerances.
However they have not made them for several years and old sets are not easy to come by on the US second-hand market. I head that
Saluc (The parent company of Aramith) bought them up as well as other competing billiard ball manufacturers.
Of course there's no reason Saluc could not make a numberless range if they wanted, as they already do this for their 3-Cushion and Snooker balls sets. I guess they just can't be bothered to, or don't think there's enough of a market for it.