According to a post
on the Epic community forums, 'gun-like' items are set to disappear from the Xbox LIVE Marketplace as a result of a new policy instated by Microsoft.
If you already own the Lancer and/or the Hammerburst, you will be able to keep those items. Otherwise, you only have until the end of the month to get them, as they will be pulled on January 1st. There is no full list of items that will be pulled, but if it's gun-like and you want it, better get it while you still have the time.
You can pick up the Lancer here
in the regular edition or here
if you prefer gold weapons.You can also pick up either a regular
Hammerburst, if that's more to your liking. Each item costs 320 MSP.