To see package names currently installed with the word “samba” in them:
dpkg -l | grep -i 'samba'
To search the currently configured respositories for “samba-libs”:
apt search samba-libs
To search for all samba and a pager for easier browsing:
apt search samba | less -i
# Then search within for lines starting with "samba":
/^samba
There may be other repositories available, but not configured. It looks like the default repositories only use samba 2, but I don’t know what other repos are available, nor what other ways there are to install samba 3 (also, since I have not worked on samba, it is possible I am reading the version wrong).