Of course there's a market in software development; just look at operating systems, games, and CAD (Computer Aided Design). In this age, it's all about software.
As for finding buyers, you need to develop software that originates around an audience, such as computer users, artists, the music industry, and the industrial industry.
I am planning to develop a software that will help grade 11 high school maths students. But I don't know where I could find the buyers. Is it possible to find buyers online?
So your audience is students? May I suggest hosting a site dedicated to the advertising of your program, along with posters of some kind that advertise your program at local schools. It's all to possible to host a website, but you would have to declare your website a business since you'd have to pay tax on whatever you earn.