Hi,
download & install the release key:
wget -qO - http://download.opensuse.org/repositories/home:/laszlo_budai:/syslog-ng/xUbuntu_14.04/Release.key | sudo apt-key add -
then add repo to APT sources eg.: /etc/apt/sources.list.d/syslog-ng-obs.list:
deb http://download.opensuse.org/repositories/home:/laszlo_budai:/syslog-ng/xUbuntu_14.04 ./
then apt-get update and you can install syslog-ng with apt ;)
regards,
Laszlo Budai