NACs on voice channels for Motorola systems are typically very close to the system ID, or subset.
for TACN (SID 2A5), possibly 2A5,2A6, 2A0, something like that.
Integrated NAC isn't set per talkgroup, it's per-site.
What's your purpose? Scanning TACN via conventional scan of the voice channels with unmute by NAC? You'll get all traffic for that site if you get the right NAC, but no talkgroup selectivity.