Spallation sources are powerful sources of neutrinos and may also provide an intense source of light new particles. We study the sensitivity of existing neutrino detectors to the decay in flight of dark states in several new physics models. I will take a critical look at models with particles lighter than the muon and pion, where the sensitivity is greatest. I will discuss in particular the J-PARC complex as well as new opportunities at the the Oak Ridge and Los Alamos spalaltion sources. The combination of these setups has the potential to improve existing limits by over an order of magnitude in some regions of parameter space. I will then highlight the needs for data acquisition and background rejection capabilities for future searches experimental collaborations.