You didn't mention this baby's age.  3 days? 5 days?  I've read about milk
finally appearing on 8th day, 10th day etc.

Feeding baby in meantime by alt method and encouraging and supporting mom to
keep pumping and nursing whatever little bit the baby will. I've had good
success in this sort of situation using fingerfeeding (gasp) with a large
tube. I don't find that cup feeding improves the baby's suck in this sort of
situation.

My theory on supplementing is - what are you trying to accomplish?  Simply
getting some calories in a baby briefly -use cup; some sort of "suck
training"- fingerfeed.  I have even put a tube under a nipple shield at the
breast-instant supply, with sucking at the right place, even though not
completely in touch with right place.  Work on that next after baby gets
idea of what to do.

 The baby may have been more affected by meds at delivery than anyone
realizes (ie: poor suck).  Tincture of time cures a lot of these problems,
if baby is fed in the meantime.  Sure hope an abundant supply appears any
moment.