There's a fanfiction where Tien and Yamcha are transported to an alternate dimension. In this dimension, they have to fight against versions of themselves that are evil. It's a really cool concept as it explores different sides of their characters and how they deal with seeing their own dark counterparts.
One possible fanfiction could be about Tien and Yamcha teaming up for a special training session. They might start off with some friendly sparring, showing off their unique martial arts moves. Tien could use his multi - form technique, while Yamcha demonstrates his Wolf Fang Fist. As they train, they start sharing stories about their past battles and how they've grown as warriors. Eventually, they come up with a new combined attack that could be used against future threats.
You can start by looking on popular fanfiction websites like FanFiction.net or Archive of Our Own. There are often many 'Dragon Ball' - related fanfictions there, and you can use the search function to specifically look for ones that feature Tien and Yamcha.
They could be part of a detective story within the Dragon Ball Z universe. Tien and Yamcha are hired to solve a series of mysterious disappearances. They start by interviewing different characters, like Bulma for any technological insights or Goku for any leads from his adventures. As they dig deeper, they find that the disappearances are linked to an ancient evil that was thought to be sealed away long ago. Using their martial arts skills and wits, they try to track down the source of the problem and put a stop to it.
Goku's understanding of different universes and races could be deepened in fanfiction. Since Dragon Ball Super introduced the multiverse concept, fanfiction could explore how Goku interacts with and learns from beings from other universes, making him more worldly and less naive in some ways.
There are a considerable number of Dragon Ball manga. It's a long-running and popular series, but the exact count might vary depending on how you classify different editions and spin-offs.