Its not that simple. You can't just recover it from nuclear reactor waste because it's mixed in with other isotopes of plutonium, and isn't in that great of quantities to begin with. So first off you have to reprocess nuclear waste to extract the neptunium - which again, itself isn't in very great quantities, it takes a lot of waste, and most places don't want to do waste reprocessing to begin with due to cost and liability issues. You then have to make neptunium targets and expose them to a neutron flux - that is, using neutronicity that could otherwise be used for power generation or other valuable purposes (it takes a lot of neutrons to make a tiny bit of Pu238). Pu238 should be more thought of as a manufactured product than as a byproduct of particular types of nuclear reactors.
Yes, I know it's not all that simple. Never suggested it was.
However, the first step in the process is still more reactors. Without the reactors, you're not going to have the radioisotopes you want for other purposes, like, say, powering deep space probes of one sort or another.
It's just another reason why we really need to get over this phobia of the word "nuclear"....