wiser heads

I am holding physical silver and wish to sell 5 kg to fund another project. (I can hear some saying don't sell physical at the moment, and I appreciate why). However the need has arrisen and it is not all of my silver.

Here?s the bit I don't understand. If Perth Mint and ABC Bullion are so short of supply, why are they only offering less than paper price for buyback? If people are successfully selling physical on e-bay for good prices, how does this make sense? OK why don't I just sell on e-bay? Because 5 kg Bullion seems to not sell as easily as smaller amounts, and E-bay takes such a slug with selling and conversion of PayPal. Does anyone know of a dealer in Australia who will buy at a fair price.
Thankyou for all replies.