It has been my understanding this year that none of the three parts manufacturers (Lycoming, ECI, or Superior) will sell a complete "kit" engine any longer. My guess is that kits were competing with their assembled engine business. Unfortunately, this puts the custom engine builders between a rock and a hard place because they have to buy all of the parts separately if you want them to build your new engine for you. It is hard for them to compete on price in a market like that - which is probably the point.
As I understand it, this is purely a business decision, and with so few suppliers in the market, the customers can take it or leave it.