maybe that guns isn't popular among the skin creators or community itself.

..i guess...most of the duel weapons dont have skins...but the duel castigos have like...3 skins i think

the normal Castigos have 3 skins

and the normal Broncos...8 skins...im not counting the Python skin cause ya know

I think the revolvers are more practical on their single version, their akimbo will make them worse because of more likely to shoot at dead enemy.

For guns with very low ammo pickup like revolvers, that is a matter.

ive done pretty good with duel broncs with the pistol perk and hitman..and this is wtihout fully loaded....and there are other unpopular or bad weapons in the game that have skins

but hey..i imagine you know what your talking about more then me..considering you have made allot of skins...even gotten some in the game..(not trying to sound sarcastic about it)

Can't speak for other skin creators, but personally I just don't like the akimbo weapons at all. They're all just rushed out with little to no thought behind it. They don't play well and some even don't make much sense. Like Kitab said already, dual revolvers are kinda useless, because you shoot 2 bullets at once and usually the first bullet already kills the enemy, wasting the other one. I think because of that, a lot of people don't like akimbo revolvers, or even akimbo weapons in general. The popularity of a weapon does affect the popularity of a skin somewhat. People think stuff like "This weapon sucks, why would I want a skin for weapon that sucks?" Noticed something like this a lot, not just in PAYDAY but also in games like CSGO.
Overkill should've just made akimbo weapons use the single variants skins.
That's just my thoughts on it.

use Super Duper Skin Swapper mod, it lets you apply any skins to any gun, including single on akimbo and akimbo on single.

hmm...