How do I find out if there is an arrest warrant on me for failure to pay CS?

Contact the court that ordered the child support.

There is no magic web site, some sites work better than other finding warrants, but in general, you can check with that court, go in and check your background record at a local police station.

In general they don't arrest you for not paying child support. That is beyond the scope of the government. But you can have an arrest warrant issued against you if you failed to appear while under bench warrant or if you fled from custody while serving time for not paying support.