A little over 60-years-ago [1942] plutonium isotopes were available to humanity only in microgram and microscopic quantitities produced
with great difficulty by Ernest Lawrence's Berkeley University atomic
smasher.
Just three years later, plutonium
isotopes were available by the pound
and kilogram as the Japanese soon found out.

I'm not saying history will repeat
itself with 6carbon(11)isotopes,
but, ironically, nuclear-reactors can be configured to "transmutate" elements
into different isotopes....and I see no
valid reason why reactors couldn't be configured to produce 6carbon(11) isotopes by neutron bombardment...if they don't do so everyday, even as you read this.
Even if natural carbon won't do as a "parent material" [or parent isotope]
when it comes to generating/transmutating
the required "offspring isotopes" in a reactor then there are other light elements on the periodic table that may do the job.

Jacob