From an answer to the linked question:
If you buy certified kosher meat then they have already removed the relevant Chelev or are selling you meat from a part of the animal in which no Chelev can be found.
The vast majority of Shochtim in the United States do not remove the Chelev because it is too time consuming (not because they don't know how). Rather, they sell the section of the animal (roughly, the entire back half) to non-Jews.
In places where Nikkur (the removal of Chelev) is still economical and practiced, I do not suspect there is any market for the pieces of fat. The one time I witnessed Nikkur taking place, all the Chelev was thrown out, except the Chelev on the abomasum which was given to a Kohein. Note that there is no prohibition on a Jew's using the Chelev as long as he doesn't eat it.