What would be the simplest way to locate the index of the third space in a string.

My goal is to get `CCC` out of this space separated list: `AAAA BBBB CCCC DDDD EEE`. where A and B and D are fixed length, and C is variable length, E F G are optional.

In Java I would use indexof, with a starting point of 10 and that would get me the third space, but it seems that I cannot do that in MySQL, so I thought maybe I could find a 'third index of' function?