Does anyone know of a citation for /k/ becoming palatal before a front vowel? Or anything that says labials are less likely than velars to become coarticulated with neighbouring vowels?
In native Turkic phonology, [k] and [ḱ] are allophones; [k] only occurs in a back environment, while [ḱ] only in a front environment. The same goes for [g] : [ǵ] and [l] : [ĺ], and no other consonant. Examples from Turkish:
[kara] 'black' : [ḱere] 'time(s)'
[ak] 'white' : [eḱ] 'addition'
In loanwords, however, this distribution is disturbed, e.g. [ḱ] can occur in a back environment in Turkish ([kar] 'snow' : [ḱar] 'profit'), but [k] still can't occur in a front environment. In Bashkir, where the opposition has shifted from [k] : [ḱ] to [q] : [k], the latter can be found in a back environment, too, but I'm not sure whether [q] can be found in a front one.
All examples off the top of my head, but can be found in probably any Turkic grammar. (Only I'd suggest, if you settle for Turkish, that you use e.g. Ersen-Rasch (in German) or Stachowski (in Polish) because all English grammars I know of are not terribly good in my opinion.)
As a counter example, in Polish, *[k] and *[g] have been conserved in all surroundings except before [i] (< *[y]) and [e], where, in the Middle Ages, they > [ḱ] and [ǵ], respectively. Examples:
*[kara] 'penalty' > [kara], *[gnetõ] 'I squeeze' > [gńotẽ]
*[kyjь] 'stick' > [ḱij], *[nogy] 'legs' > [noǵi]
*[kъlъ] 'fang' > [ḱew], *[gъzъ] 'gadfly' > [ǵes]
But, in Polish exactly the same thing happened with *[p] and *[b].
All examples from Mańczak W. 1983, Polska fonetyka i morfologia historyczna, Warszawa.