Windows 10 Enterprise Edition is only available via Volume Licensing (starts at, i believe, 5 licenses but can be any 5 different microsoft products). The other option may be to buy the Computer Hardware together with CHMI directly from ABB or an OEM supplier with the Windows 10 IoT Version pre-installed already, but in this case licenses must always be bundled with Hardware.
Hi. You will need to contact an authorised Microsoft retailer in your area to obtain a license. generally you cannot 'buy' LTSB versions as an individual as it is part of MS's enterprise offerings, given it will not automatically update and you control which patches are to be installed.