Take iridium 193 (natural abudance=62.7%) and bombard it with neutrons.
for the neutrons, just use a neutron gun (try using americium-241 from smoke alarms with aluminum foil in front of it, or better yet radium-226 from luminous dial clocks with beryllium in front of it then make a casing out of lead and poke a hole in one end of it). every Ir isotope above 193 yields beta- decay with quite low half-lives. yep, this means that within hours you'll have mostly platinum. only problem is that the only reasonably stable Pt isotopes are 190, 192, 194 196 and 198, so you'll end up with some gold and then mercury quite quickly. still, i am sure you will have quite a bit of stable Pt.