Type japanese beetle control into the Keyword Box that comes up when you click on Search the Forum in the black horizontal menu above. There's lots written here about it.
If you want the easiest, spray on, no work method, that would probably be Neem oil, available in garden stores. But be aware that Neem is not a poison (unlike your Sevin!) and does not kill on contact. The beetles ingest it and then over a period of a days it messes their systems up so they can't continue to eat or breed. So you will not get instant results, but that does not mean it isn't working. It would need to be reapplied every few weeks.
To help with next year, treat your lawn with milky spore. It is a disease that kills the JB larvae (grubs) in the lawn. Since the adult JB's are mobile, it helps if you can convince some neighbors to treat their lawns too.
By all that spraying with Sevin, you have succeeded in breeding a resistant population, so now the Sevin is useless to you (at least until an new population of the JB's move in). Sevin is harmful in the environment (kills off honeybees and lots of beneficial insects, gets into the waterways and kills aquatic life) and not very good for you and your children / pets (if any).