These forms have been seen as outdated since at least as far back as 16111, having competed with the forms con nos, con vos since the 14th century2.
However, in the Stevens' "A New Spanish and English Dictionary" (1706), the author notes that these forms were still in use in some regional sociolects:
Conúſco, Obſ. with us. Us'd in ſome parts by Peaſants.
Convúſco, Obſ. with you. Us'd only by ſome Peaſants.
In what regions/dialects were these forms used at this time, and, are they still used today?
1. Rosal (1611): "Conosco ò Conusco. decia el antiguo Castell. para decir con nosotros;"
2. Excessive Analogical Change as an Impetus for Lexical Loss: Old Spanish Connusco, Convusco
3. Convusco: a casualty of analogy, or of differential “(un)fitness”?