Where can I find the current C or C++ standard documents?

You can find the current C standard documents on ANSI web store. 

https://webstore.ansi.org/RecordDetail.aspx?sku=INCITS%2FISO%2FIEC+9899-2012

You can find the current C++ standard documents on the ISO C++ website for buying −  https://www.iso.org/standard/68564.html

The working draft of the ISO C++ standard is also available on  https://isocpp.org/std/the-standard