Are you looking to sell a component of the SaaS or just to get a partner that will help you grow the business more?
Selling a portion of the business that is profitable so you can pursue another segment is not much different than selling any other business, you are selling the assets, liabilities and income stream. To do this you need to either use a broker or find a buyer yourself.
If you are instead just looking for someone to buy in and work with you to grow the business that is a different avenue and brokers wouldn't be who I'd ever look at for that type of scenario. Essentially you are looking for a co-owner that wants to be operational, so most investors are also probably the wrong avenue and you should instead be looking for co-founder types. To do that you need to find out what skills you really need that would compliment your skills and help the business grow and you should be looking down that angle.
You might consider just hiring in a hungry new-grad or experience manager that can help scale the business but is just an employee or contractor. This way while you give up some of your profit temporarily in the form of pay to this person, in the long run you'll maintain ownership and the higher profit as they grow the business. When I got bored with a small but profitable business prior I just hired a person to run it for me. Sure they took some of the first years profits, but they grew the business and I was only involved basically for status meetings and guidance. So in the end the business became more profitable and freed me up to pursue other ventures. I would do this again in a heartbeat. It also lets you sell the business later on for a higher value usually because it is self sustained, plus you personally don't have to be committed to any long term support agreement. Usually those businesses sell easier and faster because they are less dependent on a founder operator.