I own a Stihl dealership, and the MS250 is definitely not discontinued, nor are the MS170 or MS180. Each of these models of saw is better than their replacement 251, 171 etc. The 171 and 181 are both a total POS imo, I don't even sell them in my store. Once the 170s and 180s are gone I will tell people that the 171 and 181 are good saws because I have to sell something, but until then you won't see them on my shelves.
Possibly the MS250 has been discontinued in some areas due to EPA regulations, but here we can still get them.