Guns are available on
www.gunbroker.com, however Marlin doesn't have any and isn't shipping any at present....But prices on g-b are somewhat higher than my dealer has quoted me ($539 for MX(blue/walnut),
not XLR-stainless/laminated).
Hornady dosen't have ammo, and isn't shipping any at present. However, this may change at some time in the future. (At present Hornady is the only ammo producer, but ammo is reportedly very good, but mostly suited for deer size game.) Also, Hornady is supposedly working on a flex-tip GMX for use in the .338MX.
I've got an order in for one at a local dealer, but don't anticipate him getting it through the normal channels (from Marlin, through his distributer) any time soon.
Hornady has published some loading data for the .338" 200gr FTX, though velocities and reported pressures are suspiciously low. And, unless you can get some old Hornady 200gr FN for the .33wcf, you're looking at either single loading the rifle if loaded with all other available component bullets, or casting and shooting cast bullets as no one presently has any of the .338" FTX bullets.
Also, only Hornady and Redding offer dies. Everyone is also out of the dies. However, Midsouth Shooters Supply did have some .338" Lee moulds, and a few boxes of .338"gaschecks.....