Full statewide coverage was not attained for the 2023 NAIP imagery collection. Eighteen (18) counties do not have complete coverage: 
Beaverhead, Broadwater, Cascade, Flathead, Gallatin, Glacier, Jefferson, Judith Basin, Lake, Lewis and Clark, Lincoln, Madison, Meagher, Missoula, Park, Powell, Stillwater, Sweet Grass, and Teton.

A map with the 2023 collection can be viewed at: https://ftpgeoinfo.msl.mt.gov/Data/Spatial/MSDI/Imagery/2023_NAIP/NAIP2023Collection.pdf

The NRCS has updated the 2023 NAIP county mosaics with the 2024 imagery. These are now available to download from the MSL FTP site as well.
https://ftpgeoinfo.msl.mt.gov/Data/Spatial/MSDI/Imagery/2023_NAIP/UTM_County_Mosaics/

Or you can download them directly from the NRCS here:
https://nrcs.app.box.com/v/gateway/folder/299549620165

They are named with the county FIPS code.
A map and a list of the Montana counties and their FIPS code can be found here:
https://msl.mt.gov/GIS/Boundaries

Map (PDF): https://ftpgeoinfo.msl.mt.gov/Documents/Maps/Individual/20190502_808_CountyCensusFIPS.pdf
List (Excel): https://ftpgeoinfo.msl.mt.gov/Documents/MSDI/Boundaries/MontanaCountyList.xlsx