I am here illegally in the United States, and I have never been caught. Is there any law to get a visa and stay legally in the US?

No, there is no visa. However, if you have been continuously living for ten or more years in the U.S., you are married to a US Citizen or US resident or have underage U.S. Citizen or U.S. resident children living with you, have no criminal record, and one of those close relatives has a medical condition that would require specialized treatment, you could apply for “Cancellation of Removal for Non-Residents,” Form I-42B.