Why can't I easily find the C standard online?

This is because it's copyrighted. You can buy it from the ISO website as ISO/IEC 9899:2018 for 198 Swiss franc (~$216).

For this reason, people use the last committee draft, which is otherwise identical to the standard. You can find it linked from this website using the Internet archive as N2176 for the 2017/18 version of ISO-C (aka C17 or C18). Googling N2176 yields access to other copies. The latest C11 draft is N1570.

I also recommend cppreference.com/w/c as a community reference.