  We examine the possibility that very massive stars greatly exceeding the
commonly adopted stellar mass limit of 150 Msun may be present in young star
clusters in the local universe. We identify ten candidate clusters, some of
which may host stars with masses up to 600 Msun formed via runaway collisions.
We estimate the probabilities of these very massive stars being in eclipsing
binaries to be >30%. Although most of these systems cannot be resolved at
present, their transits can be detected at distances of 3 Mpc even under the
contamination of the background cluster light, due to the large associated
luminosities ~10^7 Lsun and mean transit depths of ~10^6 Lsun. Discovery of
very massive eclipsing binaries would flag possible progenitors of
pair-instability supernovae and intermediate-mass black holes.
