Letter of Invitation Required

Hey there, I'm wanting to go travelling in China next month and have a question about the L visa. On the official Chinese embassy website, it says under 'Essential Documents Required' that:

'(2) If you are applying for a tourism and family visiting one ("L"), you will need to provide a "Letter of Invitation for Travel" issued by a "duly authorised tourism unit", or an invitation letter by a company, or a corporation, or a public institution within the border of China, or an individual.'

I'm planning on going without the aid of a tourism agency like STA travel and so how do I go about getting one of these letters if I want to do this on my own? I don't have any friends or family out in China either.