Result from Foreign Dictionaries (2 entries found)
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Sourly \Sour"ly\, adv.
In a sour manner; with sourness.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
sourly
adv 1: in a sour manner; "he complained sourly that the new
rules only benefitted the managers"