ITEAD of Sonoff fame now sells a very inexpensive Zigbee USB dongle that should work out-of-the-box with both Zigbee2mqtt and the ZHA integration

[nickrout]

And can be bought by following this thread, which lists two sellers. "Zzh!" (short for "Zig-a-zig-ah!") open-source hardware licensed Zigbee USB-stick based on TI CC2652R