I'm not entirely sure specifically about the 'tahno and korra pretty boy story' as it could be something very specific within a certain fandom. It might be a story centered around Tahno and Korra where Tahno is considered a 'pretty boy' in the context of their relationship or interactions within the story's world.
I don't know much about this specific story, but if it's related to the general lore where these characters are from, Korra is a powerful and determined character. Tahno, being the 'pretty boy', might be a character with a certain allure. He could be confident because of his looks or use his charm in different situations.
The Legend of Korra comics are definitely worth a read. They capture the essence of the franchise and bring fresh perspectives. The quality of the storytelling and the visuals make them a great addition to the series.
The 'lemon' aspect might be a bit hard to come by in a clean way as it often involves inappropriate content. But for normal Korra and Mako fanfictions, you could also try FanFiction.net. Some stories there might show their relationship developing, their adventures together, and how they support each other, which can be really interesting to read.
To be honest, I don't have an exact figure. But you can look up on popular comic book databases or ask in comic book enthusiast communities to get a clear idea of how many The Legend of Korra comics are out there.