OK I've done some searching.
where are are PA30-31 on the Due schematic?
PA30:31 are only available on the 217-pin chip.
Likewise for PE28-29-30-31, sorry there's no second SPI.
The good news is that two of the USARTs have the SCK pins broken out on PA16 (A0/D54) and PA17 (SCL1/D71).
I'm about to add them to the diagram.
Rob