If you have electric service, then you should have a good grounding/earthing solution. The utility is required to drive a 10 foot long copper rod into the ground and connect a heavy copper wire to it from the meter box. Check with the power company.
An alternative is your plumbing system. If you have a metal pipe that brings the water into the house, then that pipe is most likely a good grounding source.
Caution, many houses built after 1970 have plastic hose with only a short length of metal. Check and verify that there is at least 10 foot of metal in the ground.
If not, then most hardware stores carry or can order 10 ft lengths of copper rod that can be laid flat in the ground and buried at least a foot down where it stays moist.