Is there any way to getting work kolab's calendar plugin in roundcube 1.4?

**NethServer Version:7.9.2009
Module: webmail 1.4 from stephdl repo

If you mean kolab groupware calendar plugin I’m Pessimistic this is possible.

Kolab is special;
IIRC it stores everything (not only mails) in IMAP although it can be it uses DAV capacity of their preferred IMAP server cyrus. (NS uses dovecot for IMAP server)