Re: where in the human body is L-Dopa produced?

L-Dopa (levo-Dopa) is produced in all dopaminergic neurons in the human
nervous system since it is an intermediate in the synthesis of dopamine.

Basically, the whole process starts with the amino acid L-tyrosine being
transported across the blood-brain-barrier into the brain and the neurons
themselves. 
L-Tyrosine is converted into L-Dopa by the enzyme tyrosine hydroxylase and
L-Dopa is subsequently decarboxylated to dopamine by L-aromatic amino acid
decarboxylase.
The first process is rate limiting. i.e. it underlies strict control
through various processes, e.g. a feedback inhibition through dopamine (end
product of the biochemical chain), and signals coming from dopamine
autoreceptors on the presynaptic axon terminals.
L-Dopa itself is quickly converted to dopamine. Therefore L-Dopa levels are
negligible in brain tissue under normal conditions.

This knowledge was applied in early attempts to treat Parkinson's disease
by supplying L-Dopa which readily passes the blood brain barrier and  is
converted to dopamine in the neurons. Supplying L-Tyrosine would be rather
futile because its biochemical conversion is so tightly regulated and
therefore proceeds at a much slower rate than the conversion of L-Dopa to
tyrosine.
The motion picture 'Awakenings' gives a vivid account of these first
attempts to treat PD.

I might add that nowadays treatment also focuses on inhibiting the
dopamine degrading enzymes, so called MAO (monoamino-oxidase) inhibitors.

I hoped this helped you a little bit. 
In case you have further questions feel free to email me.