The person who found Yamato either has to be Jack or fodder lol
There's really no one else.
- King/Queen are distracted with Marco
- WsW and Sasaki both preoccupied
- Ulti is chasing Nami/Usopp, Black Maria is chasing Sanji. P1 was with but may have split off. However both were heading outside the castle towards Nami/Usopp so im not sure how they'd go from that to the storeroom.
Jack is literally the only important beast pirate unaccounted for, and if he's not on the roof its possible he went down to look for Yamato after recovering
Sidenote, also have a feeling Perospero won his battle. Oda left it off for a long time and sulong does not last that long. Potentially something good happens with that too.