https://app.mt.gov/als/index/index.html
Most people would choose a Non-Resident license. They are available in 2-day, 10-day or season pass. Keep in mind that this intended as consecutive days and the website will require you to specify your dates.
(Montana requires the additional fees for Aquatic Invasive Species Prevention Pass and a Conservation License regardless of the number of days you wish to fish. These will be automatically added to your check-out basket (see below).
For 2019, the Non-resident fees are:
2-Day fishing license $25
10-day fishing license $56
Season Pass $86
+Aquatic Invasive Species Prevention Pass $15
+Conservation License$10
