This is a relatively simple, if not automatically time-consuming achievement. Once you have access to most of your crew aboard the Thousand Sunny, continue with the story until you get a tutorial from Sanji for sending members of the crew "exploring". You'll need to choose a "Pirate Lunch" from a list, each having different effects on the length of time spent and return on investment.
Simply speak to Sanji (blonde hair, black suit) aboard the Thousand Sunny, choose a crew member, then assign a lunch, wait the requisite time, then speak to Sanji AND the crew member you sent out to complete the task (and receive your materials). The least amount of time a member can be gone is 1 real hour, so you'll need at least 12 hours spent to get this achievement.
Here's a video guide by BearlyComplete for those that may prefer one:
TA:
BearlyCompleteYT:
https://www.youtube.com/c/BearlyComplete