Karmic Infusion
http://wiki.guildwars2.com/wiki/Laurel_vendor
Take your pick, I usually get to see the one in LA. If you are buying something else as well you might consider the WvW merchant, as some things cost 10 laurels less in lieu of honour badges. That would not apply to the infusion though.
Cheers
Edit: WvW Laurel merchant, just to be complete
http://wiki.guildwars2.com/wiki/Laurel_merchant_
“Whose Kitten is this?” – “It’s a Charr baby.”
“Whose Charr is this?”- “Ted’s.”
“Who’s Ted?”- “Ted’s dead, baby. Ted’s dead.”
“Whose Charr is this?”- “Ted’s.”
“Who’s Ted?”- “Ted’s dead, baby. Ted’s dead.”