KDE SC 4.3.5 is now in karmic-backports.
The Backports repository is not enabled by default, so you may need to enable it in KPackageKit. Instructions for this are found on the help wiki.
To manually enable it, edit your /etc/apt/sources.list and uncomment the line
deb http://archive.ubuntu.com/ubuntu/ karmic-backports main restricted
When upgrading from 4.3.2 to 4.3.4, some package recommendations have changed, so using dist-upgrade (or full-upgrade in aptitude) may be needed.
Thanks to Lex for preparing these packages.