Maybe proto-Slavs in Poland, but Venedi wouldn't span Russia in 300 bc. I'd maybe place them in a small area in eastern Poland and western Ukraine, depending on what sources you go by:
I'm not an expert on the matter though, but Balto-Slavs would start their great migration only after the Germanics left a lot of territory uninhabited.
Below is a map of Europe 400 years after the start date.