It is a fact that in order to fill out Form N-400 properly you are bound to list all the trips that you have taken outside the country. There is a special table given when you are bound to state all the trip information.
As for where you can find your travel records:
All the travel records are always stated in your passport, so that you can have all the precise dates at your disposal, just by looking in your passport.
You can use your own records to attain this goal.
FOIA Request for Travel Records
In case it seems close to impossible to recover all the information that you need you can send a Freedom of Information Act (FOIA) request to U.S. Customs and Border Protection (CBP). This is a free request that it often takes up a week time for them to provide you with requested information and details.
Keep it in mind, that even if you cross the border without a stamp it is still your responsibility to report it.
March 3, 2020