Where is pollenkitt secreted?
The correct name of the coating is "pollenkitt", not "pollen kit" (I edited your question accordingly).

From the book "Biology of pollen" (Shukla, Vijayaraghavan and Chaudhry, 1998):


  The term pollenkitt is used for the oily, pigmented and sticky coating deposited on the pollen grain surface during the final stages of maturation. (emphasis mine)


That may explain why you and others struggled to find an answer in Google/Google Scholar. 

Back to your question: there are two types of adhesive coats in pollen grains:


Pollenkitt
Tryphine


Pollenkit is the most common one and, as tryphine, it is secreted by the tapetum.

According to Pacini and Hesse (2005):


  Two types of sticky pollen coat material exist in angiosperms, both produced by the anther tapetum. Pollenkitt is the most common adhesive material present around pollen grains of almost all angiosperms pollinated by animals, whereas tryphine seems to be restricted only to Brassicaceae. (emphasis mine)




Sources: 


Pacini, E. and Hesse, M. (2005). Pollenkitt – its composition, forms and functions. Flora - Morphology, Distribution, Functional Ecology of Plants, 200(5), pp.399-415.
Shukla, A., Vijayaraghavan, M. and Chaudhry, B. (1998). Biology of pollen. New Dehli: APH Publ. Corp.