It hasn't been done lately because it was something of a cult item produced for British time trialers who were pretty much exclusively a fixed gear crowd. For most folks, an internally geared freewheeling hub is the most practical choice available, offering a durable, low-maintenance, easy-to-use multi-gear platform (unfortunately most people end up wit a derailleur setup). Fixed gear riding these days is the opposite end of the spectrum which says strip everything down to the bare essentials. Efficient, light-weight, simple, comprehensible.

An internally geared multi-speed fixed hub inhabits a world between the two that just doesn't appeal to either sufficiently. Unfortunately for you, you're the outlier.

It's one thing to be able to produce a double fixed cog which is basically a CAD file and a CNC mill--cheap to make even in small numbers--and a whole other thing to talk about something like the ASC--requiring many different parts, lots of assembly, etc.