As such, is there any avenue where I can find professional referee who will be willing to look at my application and endorse my application?
It can't just be based on the application, since the purpose is to provide additional information and personal impressions. It's possible in principle to hire someone, but it's a bad idea in practice. I see it on rare occasions in the U.S., maybe once a year or so. Someone will have a letter of recommendation from an "educational counselor" or the like, who was hired to advise them on their graduate school applications. These letters are almost entirely useless. There's only so much information they could provide in principle (since the letter writer has no special expertise in the subject area and doesn't know the applicant particularly well), and the little they could say isn't particularly trustworthy due to the financial conflict of interest (they are hired to get people into graduate school, not to provide an unbiased evaluation).
As ff524 pointed out in a comment, you can ask colleagues other than your supervisor. This is not quite as good as your supervisor, since they are not in as good a position to evaluate your work (and the admissions committee will assume that you asked your friends), but it's better than nothing and might be good enough.
Another possibility for getting an academic letter is to take a single class now, as a special student rather than enrolling in a degree program, and to ask the professor for a letter once you have impressed them with your class performance. However, this could be time-consuming or expensive, and there might not be any suitable classes available to you.
