I checked, and you can't find that anywhere., thank god! It's very dangerous, and cause's atomic explosion's, and it's hurting the water by causing a high density of radiated water. It's also leaking into the ocean. It's been impossible to get, because it is hidden away from people, for our safety.
Create a neutron producing reaction, possibly using a Breeder reactor and thorium or other uranium fueled reactor. You can also produce neutrons by flooding beryllium with alpha radiation but in all cases you will need to slow the neutrons into the thermal range for adequate neutron capture. Now all you need to do is irradiate U238 which on neutron capture will B-decay twice into Pu239! Just be careful you don't get too much Pu240 as it spontaneously fissions which also produces neutrons and could have a nasty runaway reaction. And if you get enough Pu239 together it will go critical and release a huge energy flux of various radiations until enough is fissioned back below the critical mass. Enjoy!