There seem to be many ambisonic microphones popping up around the place - both high-end and mid-range commercial microphones, as well as home-built DIY microphones.
Here are some photos and links.
(all images’ copyright owned by their respective manufacturers).
On the DIY side:
In 2005, I made my own DIY ambisonic microphone using Panasonic electret capsules, which turned out to be great quality for a cost of around $300.
Earlier, Henry J. Walmsley had already built his own ambisonic microphone also using Panasonic capsules.
In late 2006, I heard of two more new DIY ambisonic mics:
Rafael Kassier’s mic built from Oktava capsules:
Probably you could find out about more diy ambi mics by joining the Sursound list.