You can buy adhesive in Starfield from various vendors and shops across the game world. Some of the most reliable places to purchase adhesive include:

• Jae Montreal in New Homestead
• Jemison Mercantile in New Atlantis
• Amoli Bava in New Atlantis
• UC Exchange in Cydonia
• Sieghart's Outfitters in Neon
• Marcel Duris in Wolf

Adhesive typically costs around 11 credits per unit, and vendors restock their adhesive supplies every few in-game hours or after you rest/sleep for a day, allowing you to buy more in bulk if needed

. For a quick and convenient option, Jemison Mercantile in New Atlantis is highly recommended since it is located near the spaceport and has a consistent stock of adhesive

. After buying out their stock, resting for a day will refresh their inventory. If you prefer not to buy, adhesive can also be gathered by foraging on planets like Gagarin (Alpha Centauri system) where you can harvest Sweetwater Cactus, or by defeating certain enemies like Brainsprout Grazers on Arcturus II

. In summary, the easiest way to get adhesive is to buy it from vendors like Jemison Mercantile in New Atlantis or Jae Montreal in New Homestead, and then rest to allow their stock to replenish.