If any of the antibodies found commercially is not suitable to your needs, some companies actually allow you to make your own. For example you can design an antigen (peptide sequence) specific to your protein (or protein from WNV) and inject into rabbit. You can collect serum in 21 days and that would be your antibody. 

Companies can immunize the rabbit for you and send you the serum. 

Or you can do it yourself. 

Other than that look at papers and test their antibodies etc.