I've seen them but they are not common. The Citori wasn't in production for very long in 16 gauge. The gun's frame was the same size as the 12 gauge so it didn't have the same appeal of a 16 made on a frame scaled to the gauge.
Claybuster is normally a good reliable source of shotgun information, but in this instance I must disagree... They are built on Browning's 20 ga. frame.
I have been shooting a Citori White Lightning 16 ga. snce 2004. Citori 16's were listed by Browning as a stock item for a few years in the 1980's and again as a Shot Show Special (one year only) I believe in 2003. They were built in many configurations, upland special and ultralight with straight grip, lightning, gran lightning and white lightning with round knob grip.
They are not especially light as 16 ga. guns go, (my Merkel is lighter) but they handle well for a Browning.
I have a match to my 16 that is chambered in .410. Stock dimensions on the 16-20-.410 guns are a bit higher at the comb than the 12 ga. version, and for me at least fit better for the rising birds most often encountered when shooting upland game.
The Citori 16's are equipped with choke tubes and can handle steel shot, but the commercial steel loads available for the 16 are best at close range, under 35 yds or so. Denser pellets like Tungsten-matrix work wonders in the 16 and turn it into a truly capable waterfowl gun in addition to its natural talents for upland game. I like mine! - but you have to be a true "nut" to appreciate a 16's subtle appeal over the more mundane 20 ga. or the utilitarian 12.
Used Citori 16's can sometimes be found for about a $200 -$400 premium over the same gun in 20 ga.