If your set-up is portable, you can roam about the countryside looking for large vertical conductors to use as antennas.
All you need is a piece of coaxial cable with a plug for your transmitter's output jack at one end and a pair of large alligator
clips at the other, plus a ground rod and a hammer. Bring along your antenna tuner if you use a high-power transmitter.
From time to time we hear of licensed AM stations in small towns closing down due to financial troubles. If this happens
in your area, it presents an exciting opportunity to borrow a full-size antenna system. You might try approaching the station
owner and saying that you want to lease the antenna field for some credible purpose (astronomy, grazing cattle, whatever you
can think of), or say that you make a hobby of listening to distant stations and you would like to rent the antenna for receiving.
Then clamp on and radiate!!! AM stations that sign off at sunset might present a similar opportunity.