Sousaphones, marching tubas, concert tubas? Budget? Tubas have far more variety than any other brass instrument, so you need to help us help you by giving more information about what the school's needs are. Budget is the most important, since even beat up school tubas can cost thousands of dollars. If you can post that I might be able to locate something near you that fills the needs of the band program. Probably not, but I can poke around. Also, are they willing to pay shipping? That will greatly magnify your/their choices. Also, have you tried searching all of CraigsList at once using SearchTempest? I use that a lot and it can be really helpful. Enter your zip code, select which category you want to search (for instance Musical Instruments) and enter some keywords and the mileage from you that you want to search. It will search all CraigsList locations within your selected distance. Very handy! If you simply enter "tuba" you will get a lot of hits, but some will be sousaphones, some will be concert tubas, very few will be marching tubas or decent quality convertible tubas (which I would avoid, anyway). Further, tubas are most commonly found used in BBb, which is what schools use, but they are made in four keys: F, Eb, CC and BBb, so you need to make sure you are looking *only* at BBb tubas. If you want any additional assistance, contact me via the private messages and I can give you some other places to look. Good luck!
Wade