I'm not sure specifically as I haven't read it in detail. But generally, a light novel might be about various things such as a unique tournament system, different characters competing in the goumon tournament. It could involve elements like character growth, different strategies in the tournament, and the relationships between the competitors.
The 'goumon tournament web novel' might be centered around a tournament where various competitors from different backgrounds come together. It could have elements of action, adventure, and strategy. There may be a complex plot involving the relationships between the participants, their goals in the tournament, and the challenges they face along the way. For example, they could be fighting for a grand prize or to prove themselves in a certain way.
Since I haven't actually read the 'isekai goumon hime light novel', I can only make educated guesses. The 'isekai' aspect sets the stage for a story set in a different world. The 'hime' gives the idea of a female lead with perhaps a noble or important position. The 'goumon' is a bit more difficult to pin down without more context, but it could suggest that she experiences some form of cruel treatment or difficult trials in the story. Maybe she's a princess from our world who is thrust into a brutal isekai world and has to use her wits and any special abilities she might have to survive and thrive.
Online platforms like Amazon are a great place to start. They usually have a wide range of light novels, and there's a good chance the 'goumon tournament light novel' is available there. You can also check other online book retailers specific to Japanese or light novel literature.
You can try looking for it in specialized bookstores that carry light novels. Some large chain bookstores might also have a section for light novels where it could be available.