The NB IoT network is available in the countries highlighted/listed below
The map below shows NB IoT networks around the world as of January 2020
As of Jan 2020 GSMA (link to GSMA site) had identified:
69 operators in 141 countries investing in NB-IoT networks with 93 national networks switched on.
See list of global telco's with NB IoT switched on and their bands and MHZ ranges by clicking here
NB IoT Network Map
New NB IoT networks are being switched on in new countries on a weekly basis. See the table and map below for which countries have full or partial NB IoT networks switched on.