You might have limited resources and so much on your plate and that's normal. However even if you have a lot of work with your existing clients, there's a way to make time for new ideas.
Focus on the customers who bring you more money. Make sure your other customers are aware that you'll be spending less time with them and be prepared to loose them.
Now you have a bit more time, find more of the better paying customers and find ways to sell more to them.
Eventually ask them to promote you to their network. Be ready to build new partnership to boost your growth and welcome new opportunities if they're within your strategy.