Choose your large car dealerships especially chains in rural areas, they usually take huge cash sales and pretend not to know anything and definitely don't claim it on their taxes. Where I live they boast about it in public all the time.

Pretty much any company that's cash only and has a monopoly of an area is a good pick, towing, utility, large tree cutting, some factory farms, manufacturing (esp of parts that go into arms/specialty weaponry) and chain medical, big contractors that offer services for HOAs and it must go through them, professional cleaning services. That's very broadly of course.