Interesting pairing! Lucario x Zoroark is a bit niche compared to more mainstream Pokémon ships, so you have to know where to dig. My recommendation is to head straight to Archive of Our Own and use the pairing filter. The tagging system there is superior—you can filter by kudos, which is their equivalent of likes. I’d sort by ‘kudos’ and maybe add a word count minimum to avoid snippets. The quality varies wildly; some writers go incredibly deep on the aura vs. illusion dynamic, while others just want them to cuddle. A lot of the really thoughtful stuff gets buried under quicker, fluffier updates on other platforms.
Don’t sleep on FanFiction.net either, even though its search is clunkier. The trick is to search for stories with both characters tagged, then sort by reviews. The community there is older and some of the long-form epic takes on this pairing are from years ago, still sitting with high review counts. I found ‘Aura’s Illusion’ there, which is basically the gold standard for this ship—explores their roles as rare, almost mythical Pokémon in a really dark, grounded Sinnoh. You just have to wade through more abandoned fics.
Tumblr blogs can be surprisingly good for shorter, character-study pieces, but it’s a real treasure hunt. I sometimes just browse the ‘Lucario’ and ‘Zoroark’ tags and stumble upon a great one-shot. The best-rated ones tend to migrate to AO3 eventually anyway, so that’s still my first stop.