The extremely low demand for certified systems is why Technocarb hasn't renewed their EPA certificates or obtained new ones. As well, EPA or CARB certificates aren't required for conversions in Canada. Their ESIP Parts Package is available in both LPG and CNG (read to the end of the brochure) and the main difference is the use of a different regulator.
New
EPA regulations have recently been released and EPA-certified conversions are only available for new vehicles. Older vehicles (older than 2 years) are out-of-luck.
EPA Regulations aren't very clear but there has been discussions on CNGchat that seem to indicate that a CNG conversion is legal if it doesn't tamper with existing emission controls and if the tailpipe emissions are not dirtier.