Find Commander Samaul in Dustwallow Marsh.
The beginning of every month the Kul Tiras Marines all get paid and usually leave Theramore for somewhere else. A lot of them come here to womanize, carouse, and just have a good time. One of those groups I'd consider regulars here at the tavern, and I believe this Hendel is among them.
Commander Samaul in Theramore would be able to help you find him if Hendel's still stationed there. He's completely loyal to Proudmoore, but if you drop Elling's name, he should help you out... discreetly.