Fermi-arc surface states of Weyl semimetals exhibit a unique combination of localization to a surface and the connection to the bulk Weyl fermions. We predict characteristic quantum-oscillation signatures of Fermi arcs in the tunnel mangetoconductance across an interface between two Weyl semimetals. These oscillations stem from a momentum-space analog of Aharonov-Bohm interference of electrons moving along the interface Fermi arcs, driven by an external magnetic field normal to the interface. The Fermi arcs' connection to the bulk enables their characterization via transport normal to the interface, while their localization along the transport direction manifests in a strong field-angle anisotropy of the oscillations. This combination distinguishes these oscillations from conventional Shubnikov-de Haas oscillations and makes them identifiable even in the complex oscillation spectra of real materials.
