Is there a Naruto is Goblin Slayer fanfiction available?
Well, it's possible. There are a ton of fanfiction works that cross different anime or manga universes. Since both Naruto and Goblin Slayer are quite popular, it wouldn't be a surprise if someone has written a fanfiction where Naruto exists in the Goblin Slayer world. However, the quality and content can vary greatly. Some might focus on Naruto's skills in the Goblin Slayer setting, like how his ninja abilities would fare against goblins. Others might explore more of a character - based story, like how Naruto would interact with the characters from Goblin Slayer.
There probably is. Fanfiction is a vast and diverse world where fans get to explore their wildest ideas. The concept of Naruto being in the Goblin Slayer universe is an interesting one. In such a fanfiction, we could potentially see Naruto using his shadow clones to take on hordes of goblins. Or perhaps he'd form an unlikely alliance with the Goblin Slayer himself. It really depends on the creativity of the fanfiction author. You might need to dig around a bit on different fanfiction platforms to find one though.
Yes, there are likely some Naruto is Goblin Slayer fanfictions out there. Fanfiction writers often like to combine different popular franchises in creative ways. You can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own.