  Current matched-filter searches for gravitational waves from binary
black-hole mergers compare the calibrated detector data to waveform templates
that omit the higher-order mode content of the signals predicted by General
Relativity. However, higher-order emission modes become important for highly
inclined asymmetric sources with masses above $\simeq 100 M_\odot$, causing
current searches to be ill-suited at detecting them. We present a new
gravitational-wave search that implements templates including higher-order
modes, adapted signal-glitch discriminators, and trigger-ranking statistics to
specifically target signals displaying strong higher modes, corresponding to
nearly edge-on sources with total redshifted masses in the intermediate-mass
black-hole range $M_T(1+z) \in (100,500) M_\odot$ and mass-ratios $q\in(1,10)$.
Our search shows a volumetric sensitivity gain of up to $450\%$ to these
signals compared to existing searches omitting higher-order modes. We deploy
our search on public data from the third observing run of Advanced LIGO. While
we find no statistically significant candidates beyond those already reported
elsewhere, our search sets the stage to search for higher-mode rich signals in
future observing runs. The efficient detection of such signals is crucial to
performing detailed tests of General Relativity, observing strong-field
phenomena, and maximizing the chances of observing the yet uncharted realm of
intermediate-mass black hole binaries.
