ESA is getting serious about starting their own RTG production, with one official saying:
Southwood said in an interview with Spaceflight Now. "We are building for a pretty major capability being available in Europe in the 2020s."
However, ESA is looking at using americium, which produces less power and more neutron radiation. No explanation is given as to why that and not Pu-238.
NASA does not have enough Pu-238 for JEO currently, but will if the contract to buy plutonium from Russia can be renegotiated. Russia wants more money since they have the monopoly on plutonium. If those contracts are fulfilled, then there will be plenty for JEO.
Still waiting on approval of US restart of Pu-238 production.