What are these wires called?
If they are an intentional part of the design they are jumper wires. If they are to correct a mistake in the design they are bodge wires.

They aren't anything special, just wire. They look to be in the range of 24 to 30 AWG and PVC jacketed.

You can buy it in any electronic store.

You can also salvage it from things like old SCART cables and similar things.