Basically what you do is find the pokemn you want to capture on the dex nav.
Then Catch it (if its shiny or not) to add it to the dexnav search system.
Then on the Dexnav screen tap the Pokemon you want to chain and hit search. This will guarantee that Pokemon in a shaking grass spot. just keep doing this and over time shinies will appear.
Tynamo - Mirage Caves: South of pacifidlog, North of route 132, North of fallarbor, north of fortree, and west of rustboro.
Larvesta - Mirage Island: Route 114 Mirage Forest: North of route 111
Audino - Mirage Forest: south of route 132, south of route 109 Mirage Island: south of pacifidlog Mirage Mountain: east of mossdeep,
Hope I Helped