Delicious natural sources are whole eggs and the fatty animal meat. In certain neurons, choline is metabolised into acetylcholine; the extra acetyl group is donated by acetyl-CoA (which draws on the inexhaustible supply of acetate anions which are constantly burned in the citric acid cycle).
The choline acyltransferase enzyme is responsible for catalyzing this process.
It happens in the body of the neuron, and the finished acetylcholine is transported in vesicles via axoplasmic flow.
This acetylcholine is an ester of acetate and choline.
Once its job in the synapse is done, synaptic acetylcholinesterase breaks it back down into acetate anions and choline.
This hydrolysis takes less than a millisecond.
The acetate goes god knows where (presumably back into Krebs cycle) and the choline is dutifully reabsorbed by its uptake transporters ( of which there are two, one Na+ /Cl- dependent high affinity transporter and another independent transporter of lower affinity).
This reuptake is the rate-limiting step in acetylcholine synthesis.