I-130 for Brother - Do not remember I-94 number for visit 16 years ago

[kof]

My brother visited US on B-2 visa in 2000. Now we do not have the copy of that I-94. We tried to get the number from USCIS site with no success.

I-130 forms requires to enter I-94 number. Is the passport records and old Flight tickets copies sufficient?
Can I leave blank for I-94 form? We're trying to get the I-94 number and it's really old information.

Any suggestion while filling out I-130 form?