If you'd like to buy any of the Stable Elements, Alfa Aesar sells most of them.

Here's a problem that really *bugs* me: the
Stability of the Atom. I made a chart of the stable and semistable
isotopes. The table is arranged by the excess number of neutrons.

Could quarks explain the above table? You
can read up on quarks at the Particle
Data Group page. The page is aimed at non-physicists, and is
delightful. For physicists, you might enjoy *The Weak Interaction
in Nuclear, Particle and Astrophysics* by K. Grotz and HV Klapdar --
it's a very hard book. Let's suppose quarks exist, and that a simple
explanation exists for atom stabililty. Maybe, each Proton (uud)
and Neutron (udd) can be considered as a *triangle*. The problem
would become geometric. Why is it that Stable Isotope A frequently
can be made into Stable Isotope B by adding two protons and two neutrons?
Perhaps because Helium-4 (2p 2n) is a tetrahedron, and adding a tetrahedron
often doesn't affect stability.