I blew the dust off of an old SCO and ORC which may be close to what
you're looking for:

SCO:
    f1 0 4097 10 1

    ; couple of flies buzz around
    i7 77.0  5.0  7.06 300
    i7 77.2  4.6  8.00 200

ORC:
    ; Insect buzz cosine-term instrument
            instr   7
    ipch    =       cpspch(p4)
    inhm    =       int(sr*.5/ipch)
    krdm    randi   .1,ipch*.0333,frac(p2*.7071)
    kpch    =       ipch*(.9+krdm)
    kenv    linseg  0,p3*.3,p5,p3*.5,p5*.5,p3*.2,0
    abuz    gbuzz   kenv,kpch,inhm,1,.925,3
    aout    reson   abuz,ipch*24,ipch*12
            outs    aout,aout
            endin

No guarantees; I used this exactly once as an anti-climax in something
I wrote a decade ago...

		-Ed

Hi,

I've been trying to put together some instruments that duplicate the sound
of buzzing insects.  I'd like to get a fat house fly type of buzz as well as
a more high pitched mousquito.  I'm currently  mostlly working with VAZ but
I use Csound as well.

Thanks

--Mark