Rural property is usually listed as a lot. 40 acres is the most common size in my area--most of the original 40 acre plots have stayed intact and not been broken up.

I bought it in a pretty traditional manner.

Here's a site selling acreage in southern Missouri starting at under 2k/acre: https://www.landwatch.com/missouri-land-for-sale/southwest-r...

My neighbor's 11,000 sq-ft house sits on two 15 acre lots. You buy the land in places where a 40-acre lot isn't considered unusual. IOW, pretty much anywhere that's not a city or a suburb of a major city.

As for the "how," you contact a realtor who specializes in rural properties and tell them what you're looking for.