There are many large pacels of land in the Ag Reserve in Montgomery County, so finding a 40 acre parcel is doable depending on your price range. Getting county approval to run a business like this in the Ag Reserve would be much more difficult. Your search should also include Frederick County. Good luck.
First, I'd find a buyer broker (realtor) to set up a search with your specific requirements. This will immediately give you access to anything that's currently on the market . Thereafter it will notify you of anything new that comes on the market the very same day. Next, have your realtor put out "feelers" in the community in which you wish to find your property. Many good properties are found by word of mouth connections through churches and community groups. I would truly appreciate the opportunity to assist in your search. I have found several locations for church groups and know the county quite well. My cell number is 301-996-2924. Regards, Chuck Bailey