well known retailers for this unit and all the other recording gear you would need, including mics and such, are:
sonicsense.com
cascademedia.net
oade.com
micsupply.com
as for why you need the additional gear, with the microtracker you will need to patch a signal from a taping rig to your unit, all this Microtracker does is record a signal, it of course does not have mics or anything else, its just a recorder, so if there are no tapers at a show and you show up with your Microtracker you will not be able to record the show, which is why you really need all of your own gear in addition to the Microtracker unit