Histamine is mainly found within storage granules of mast cells but also found in other tissues like:
Histamine is mainly found within storage granules of mast cell but also found in other tissue 

Mast cell histamine – mast cell and basophile. 
Non mast cell histamine – Gastric mucosa.
Gastric mucosa.
Oral mucosa.
Inner epithelium.
All of the above.