There's not much point hanging around waiting for somebody to pay you to write about music. And if they do, they'll probably ask you to write about something you don't have much interest in.
Why not just write what you want for the love of it? Lots of people do it and some of them are big names.
In The Blue Moment Richard Williams writes about some of the musicians whose paths he has crossed throughout a long career as journalist and a&r man, touching upon areas of music beyond the well-trodden paths. It's thanks to him I'm listening to a record Burt Bacharach made with Ronald Isley in 2003. I'd never heard of it before.
Andrew Collins won't mind me saying he's a very methodical sort and therefore it's not surprising to find his music blog aims to pick "the 143 best songs in the world". It's more light-hearted than it sounds.
Finally Paul Burke writes short entries about something that's just happened to him - he saw Paul Weller in the street, he watched a test match, he noted American Independence Day - and comes up with a song it brings to mind.
In the old days of paid work nobody ever asked them to write material like this, which is why we didn't get to read it.