The best spawn for Pirate Corsair would be in Krailos. This is a mini world change that is not announced so the only way to see if it is active it is to go and check.
If this world change is not active the next best spot would be in the upper floor of Nargor during rapid respawn.
I completed the 1000x in Krailos spawn, however this spawn is random, so may need to check daily in case pirate ship is there.
You can watch this video for more information:
Question Revival II contest - winners! - YakiHon check pleaseFebruary 08, 2021
Third Anniversary InfographicDecember 28, 2020
Looking for a community managerJune 09, 2019