I wonder - most satellites are covered with silver or gold colored foil as
a solar reflector - but it's usually not smooth, so you would get a fair
diffusion there. I don't know about solar panels..
GPS and suitable software that can access a database of geosynch satellites
should be able to aim the transmitter and reciever optics at the same
satellite. You would need both transmitter and receiver to agree on what
bird to aim at.
The lunar retroreflectors are corner cubes, so there's much more
directionality to the return beam. A diffuse reflector would be wasting a
large proportion of the incident beam.
Possibly, a first step would be to use a CW laser, and on/off modulate it
with the modulation bits tied to an atomic timebase - you can get the
timing signal from the GPS system - and the receiver would be synchronous
to the transmitter. Hams have used similar schemes for years to get
reliable communications in very high noise conditions..
Chuck Kuecker