There is a small market in Norwalk, CT on Route 1, just north of Stew Leonard's, sort of across from Post Office. Name is Taste of Europe. Mom and Pop-type couple just took it over 3 months ago. They have a small, but good selection of deli meats and sausages, as well as breads, candies, sauce mixes, etc. They appear to cover Polish, German and possibly Hungarian foods. I don't know about Czech. Worth a shot. Otherwise, there is a Polish market in Stratford, and one in Bridgeport...I've been to both, if you need more information on them.
Milans is a Slovak restaurant close to Greenwood Cemetary in Brooklyn. They have a small market offering Slovak food items check out their website for a list of what they carry.
Down the street from Milans is Eagle Provisions, they usually carry Slovakian beer.
There are small Slovak communities in Passaic NJ, Yonkers NY, and Bridgeport CT.
In Riverhead NY there's a market on Old Country Road that I read or was told has eastern european products,I know there is a significant Polish community in Riverhead and they may carrie some imported products I was told also Ridgewood/Glendale NY has various citizens from Poland, Romania ,Albania so maybe. There are local newspapers as well as the Village Voice (the Daily News,Times etc with neighborhood profiles