Nobody has this item because it has not ever been released.
If you go to the BLI website and check out the delivery schedule, it is now one of several items listed as "To Be Determined".
I would translate that to they have no idea when they'll be able to actually produce it--or if they do they don't want to disappoint people any longer by quoting a date and then having the date slip.
The MTH GS-4/GS-6 looks great, runs great, sounds great, and smokes well. However, if you are a purist, the drivers are undersized for the GS-4 version but closer in size to (but still larger than) the GS-6 prototype version. This is a big engine with a big rigid wheelbase! It does not like 26" radius curves unless they are superelevated slightly, and it does not like any little dips or vertical grade breaks in a horizontal curve--it has a slight tendency for the front axle to lift up and out over the outside rail at such locations. This can be fixed by adding more weight to the front of the boiler. I opted to fix my trackwork instead.
The SP purist may see a few details on the GS-4 model that might be more correct for the GS-6 and perhaps vice versa. The model still looks great.
On my Kato 26.375" radius curves with 28.75" radius easements, the MTH 4-6-6-4 and 4-12-2 both track better than the 4-8-4 (though I usually don't run them as fast as a 4-8-4). I was able to get the 4-8-4 up to 80 scale mph on my curves, after improving the trackwork--but at higher speeds it may still derail. I did not add extra weight to the boiler as some others have done because I wasn't sure how to get it apart without damaging the beautiful paint finish.
John