What's a Bouzouki? MIDI has no idea!
All midi knows about is various methods of selecting a sound/instrument. All midi has available is a number, or a sequence of numbers. What those numbers produce is entirely dependent on the devices attached to midi.
You don't bother to say what your sound source is. Computer? Tone Module? If the latter, which one?
You refer to a list of 127 instruments. 127? If you're referring to the list of GM instruments, there are usually 128, although they are activated as 0 thru 127. Most midi devices may have many more instruments than that available, but you need to use extra codes to select different banks (or sounds) as well as specific instuments in a particular bank.
Does the sound source you're using include a Bouzouki. The standard GM list does not, I'm fairly sure. Your device may have one, in another bank?
If your device does NOT have such a sound, then you have options. If your device allows the uploading of samples, you could sample (record digitally) a bouzouki sound, and add that sample to the sounds available on the device. Assign the sound to a number as appropriate to the specific device, and use that number when playing your midi data.
If the device has something close to a bouzouki, then you could edit the parameters for that instrument until it soulds more like what you want, save the new patch (many devices have 'user' memory for doing just that) and then use the new patch on your playback.
Another option is to find a module, or whatever, that already DOES have a bouzouki somewhere (even 'hidden') on it's sound/patch lists, and work out how to select that (again, prob need to select bank, then select instrument.
If I had more information, I could prob be more helpful.