  Superluminous supernovae have been proposed to arise from Population III
progenitors that explode as pair-instability supernovae. Pop III stars are the
first generation of stars in the Universe, and are thought to form as late as
$z \sim 6$. Future near-infrared imaging facilities such as ULTIMATE-Subaru can
potentially detect and identify these PISNe with a dedicated survey.
Gravitational lensing by intervening structure in the Universe can aid in the
detection of these rare objects by magnifying the high-$z$ source population
into detectability. We perform a mock survey with ULTIMATE-Subaru, taking into
account lensing by line-of-sight structure to evaluate its impact on the
predicted detection rate. We compare a LOS mass reconstruction using
observational data from the Hyper Suprime Cam survey to results from
cosmological simulations to test their consistency in calculating the
magnification distribution in the Universe to high-$z$, but find that the
data-based method is still limited by an inability to accurately characterize
structure beyond $z \sim1.2$. We also evaluate a survey strategy of targeting
massive galaxy clusters to take advantage of their large areas of high
magnification. We find that targeting clusters can result in a gain of a factor
of $\sim$two in the predicted number of detected PISNe at $z > 5$, and even
higher gains with increasing redshift, given our assumed survey parameters. For
the highest-redshift sources at $z \sim 7-9$, blank field surveys will not
detect any sources, and lensing magnification by massive clusters will be
necessary to observe this population.
