Are the cables available from the dealer or factory?
Materials should be. Is (by heart) ISO 2020-A-32 steel core cable 3,2 mm
dia, Nicopress. But check that.

Or can they be made up by an AI/AP?
That too.

Are there tricks for doing the replacement?
Use the old cables to pull through the new ones. If you loose the cable in
the rear fuselage, or it gets jammed in the guides, it usually requires
holes to get to it. And replace any Tecalan guides in the S-tubes of the
pedals while you are at it. Significantly reduces future cable wear.