Several options available
Technically ... all the Squirrel hardware is custom manufactured at their Vancouver head office
Such as the opto-isolation modules (rs232 or rs422 cards) are only made there, they don't exist outside of Squirrel
The only place to purchase the hardware would be through one of the direct offices (Atlanta, San Fran, Vancouver, Long Beach, or Chicago)
or through one of their many business partners across the globe