The Facility's services have been available to anyone with a large enough wallet. They've picked up a clientele that ranges all over the spectrum of the underworld to even contracts from politicians and governments the world over. Many of which have been for X-23's assassin and retrieval skills, but not all. Some have hired the Facility to create for them a specialized genetic weapon.
On the cover of X-23 v1 issue 3, we're given a glimpse of all the people who may have hired X-23's services from the Facility. Many more are also not revealed. Some of these faces on the cover may have never been clients of the Facility too. Not all are revealed inside the pages as to having placed bidders. Magneto, Dr. Doom, and Apocalypse are three that may have just been used for cover reasons as they have never mentioned or shown any prior knowledge to X-23's existence in any story.
For certain at least, as of the completion of her first test mission assassinating the Johnson candidate, we're shown 15 screens of potential clients. As her reputation grew in the underworld, those numbers may have grown. The people shown this early on include such faces like Hammerhead, Hydra, the Red Skull, Mr. Sinister, Wilson Fisk, Advanced Idea Mechanics, among many many more. (How many do you recognize?)
Wilson Fisk, the Kingpin, gets name dropped directly even during this X-23 v1 issue. Later on it's followed up with what one of his missions was in X-23: Target X.
X-23 has handled all manners of operations including a raid on an A.I.M. complex. She's taken out drug lords, crime bosses, politicians, warlords, dictators, godfathers, and the list goes on for miles. Over 3 years worth of missions is suggested in the origin miniseries. Thousands of kills as suggested by Dr. Sarah Kinney. How accurate this number could be is entirely unknown. During New X-Men: Academy X, it's even pointed out that she's done missions in Afghanistan.
Much later after X-23 escaped, the religious zealot group known as the Purifiers hired the Facility's services to create them a weapon. This, alongside the comments after the Wilson Fisk hired mission, helps suggest the Facility not only sold X-23's services out, they also sold their own services out in creating genetic weapons of a wide array. Many of such weapons could be dictated by client requests as the creation of the Predator X project had shown. It is unknown how many genetic samples of powers the Facility may have in their possession. Nor is it known how many were destroyed when X-23 herself escaped.