I assume that you want to build a "Walsh-type" omni speaker with purchased drivers. Otherwise, you've got quite a project on your hands, per the post above. Ohm uses - what appears to be - a more conventional driver than the original Walsh design and adds a tweeter (again, per above). I don't know where you'd find available drivers suitable for this type of design, but, if you want to go the original full range Walsh route...
You might try here:
http://www.hhr-exoticspeakers.com/HHRhome.htm
I believe that this guy is actually manufacturing Walsh type drivers of the original multi-banded design.
You might try here:
http://www.hhr-exoticspeakers.com/HHRhome.htm
I believe that this guy is actually manufacturing Walsh type drivers of the original multi-banded design.