Official source from Department of Labor:
Question: How do employers get a prevailing wage if filing an H-1B, H-1B1,
or E-3 Labor Condition Application?
Answer: The Immigration and Nationality Act provides that, unlike the other
labor certification programs, the employer has the option of using one of
three sources: (1) requesting a prevailing wage determination from the
appropriate SWA; (2) using a survey conducted by an independent
authoritative source; or (3) using another legitimate source