Not sure about Montana.There are some out there, but not as many as there used to be.Here's why:
Back in 93, during the Klinton era,the gun dealer industrywas losing money to "Kitchen Table FFL's" like you want to be because they had no overhead costs so could sell substantially cheaper! The dealerspressured the ATF to do something to regulate them more.
What they basically did was say that as an FFL since you are making a substantial part of your income as a dealer from the sale of firearms, you are therefore running a business - subject to all the local restrictive business zoning laws, etc. Now you have to have proof that your home/businessis in the proper zone.
If you can be zoned, you can do it.