I have found the best way to get clients is to go out and meet people. Local networking events work well.
always have some business cards on you, if you come across any tradesmen drop it into conversation (I say tradesmen as they are often soletraders and in charge of who they outsource to)
Go to your local branch meeting and meet other bookkeepers in your area, take on some sub-contracting work, or often one bookkeeper will pass on potential clients. Come to summit to get ideas and contacts.
One of my branch members has had some success from Bark so may be worth a try.