The one issue I always have with ebay and Tri-X is that I see people want to have more money for their expired Tri-X then I pay for my fresh Agfa APX/Rollei Retro. Of course the film was more expensive in the first place but still, it comes of as a little strange ...
But generally EBay is quite a nice place for film, and if it doesn't have to be Tri-X I would recommand having a look at AGFA since their b/w-stuff is quite good. Unlike their colourfilm, that was rather ... well I don't want to speak ill of the dead. Bad, ok thats what I thought it was. However I don't really know how things are in the US, here in Germany/Europe there are companys with the rights to AGFAs films (agfaphoto is one brand, but the films branded Rollei Retro are really close too) so they are widely available and come at about 2,80€ a roll even for single rolls.