I couldn’t find any cleared saves for the demo in my searches, so I grabbed the SDK Config tool to play with the RTC and made one myself. Exported with JKSM, so pretty much just unzip, drop “Pokémon_Sun_&_Moon_Sp__Demo” into the /JKSV/Saves folder on your (micro)SD card, and you’re good to go. Save is named “CLEAR_ALLEVTS”.
Save created and dumped using a US n3DS running Luma3DS on a 11.2-35U Sysnand – I forget if the demo was region-free, so ymmv on other regions.
This save has all events triggered and all items unlocked, meaning you can transfer the following to the full game:
Stardust x 3
Pretty Wing x 10