I don't think there are any seasonal (annual) killifish in Maryland, just non-annuals, and most types native to the state are really more from brackish or saltwater than fresh. There is the rainwater killi (Lucania parva), which sounds like a freshwater fish, but is actually not.
If you don't need it to be a true killi and are just looking for a small native species for tubs, I'd suggest Rosy Red minnows which are super cheap and available at most local pet stores usually sold as feeders. These are the the xanthic form of the native fathead minnow and you can usually find the native coloration in among the "reds" if you'd prefer that are closer than what would be naturally occurring. I've used them in small tubs for years and they will winter over in a pond if you'd like or keep them inside in a tank over winter if your tubs will freeze solid.
If you want to try to find fathead minnows from a local native population if looks like there are a couple of places they've been collected in our area.
http://fishmap.org/species/Fathead-Minnow.html
