Asparagus is actually quite common in a few of the zones before the stretch of level 70 + zones but since it is commonly used in raising the Chef profession the price of the item makes it worth going out of your way to farm for either to use or sell. The two best farming locations I know for Asparagus are Mount Maelstrom coming it at number 1 (the first picture just below) and the second best would have to be Fireheart Rise's farming location. Fireheart Rise also has Raspberries which will sell for a lot on the Trading Post.
Northern Mount Maelstrom in Gauntlet Gulch by the Gauntlet Waypoint.
Southern Mount Maelstrom in The Stylchs. Closest Waypoint is Judgement Waypoint to the east.
This is in the center of the zone, closest waypoint is Vorgas Garrison but it is usually contested so what I recommend is you take is Rustbowl Waypoint to the west by the Frostgorge Sound level 80 zone. This will take you by two more Raspberry spawns and also quite a few other goodie spawns for gathering. Also you'll venture by a ton of Hyenas and if you have some Magic Find food on you'll be sure to get quite a few blues. They're really easy to AoE down!