How can I tell which flights on United from Newark to LAX have the lie flat seats?

How can I tell which flights on United from Newark to LAX have the lie flat seats in first class?

Traveling outbound from Newark to LAX on Aug 7th and returning from LAX on Aug 8th if that helps.

I have seen postings that some of the 757-200 have that, but when I look on SeatGuru even though it is labeled as BusinessFirst they look like standard first class seats.

Thanks!