Well, another place to look could be some Naruto - centered fan communities on platforms like Reddit. There might be fans who have either written or know where to find such fanfiction about Naruto and Yuna kissing. However, make sure to follow the community rules when searching.
Some Tumblr blogs dedicated to Naruto fanfiction might also have what you're looking for. These blogs often share and recommend different fanfictions. You can search for tags related to Naruto, Yuna, and kissing to narrow down the results.