This is the build I use for burst damage orientated Sona as a support. It isn't meant to be an ideal build, though I want to pursue it. I update the guide as I test things out myself. Advises are always welcome.

DOMINATION
Dark Harvest: Not initially as good as the other keystones, but it still offers decent damage when timed right. Its greatest benefit comes late game, so try to farm soul essences whenever possible when it doesn't hinder your team too much. You usually get enough souls from the lanes and team fights.

Taste of Blood: I took Cheap Shot instead of this at first, but without something to trigger the effect, the damage remains low. Dark Harvest makes up for the damage. With Taste of Blood your sustain and chance of survival is better during fights. I suggest taking Cheap Shot if you have an ADC like Ashe with you, who can help to trigger it.

Eyeball Collection: It doesn't give an initial damage boost, but it's the only rune here that gives damage. You can pick vision as well for the utility.

Ravenous Hunter: Same as with Taste of Blood, though no initial benefit. Ingenious Hunter is a good option if you are comfortable enough without the extra healing. Ingenious Hunter reduces the cooldown for Hextech Revolver's passive, meaning more damage.

SORCERY
Absolute Focus: More ability power means more damage, and you get some from the start.

Scorch: Burst damage. Good for poking during the lane phase and later.

Hextech Revolver: A bit weird pick at first glance, but I focus on dealing burst damage, so this is an ideal item for me. No need to worry about activation either. Cheap to get and you can upgrade it later if you have extra money. No match has lasted long enough for me to upgrade it yet.

Rod of Ages: I'm not much of a fan of Zhonya's Hourglass and alike, so I rather get this. The hourglass relies on activating it at the right moment while Rod of Ages gives you a bunch of health right away and more later, along with other benefits. More ability power later on means more damage as well. You can take the hourglass if you find yourself unable to survive opponents' dive and what not.

Exhaust can be changed to Ignite if the opponents don't have a champion or champions that have fast basic attack. I might consider taking it if the opponents don't have a tank on bottom lane and the only fast basic attack is at another lane.