Of course they weren't willing to sell. Slaves were the labor force for the south. AND even if slaveowners had sold their slaves to the north, what would stop them from buying more? Ron Paul is an idiot who couldn't think his way out of a paper bag.
The fact that importing slaves had been illegal for 50 years?
It should be obvious that any offer to buy the slaves would have been contingent on the fact that slavery would end. The importation of slaves had already been outlawed long before the civil war era. You are attacking a straw man here.
There would be no slaves to buy. Importation of slaves was against law in the US and had been since the early 1800s.