Three brand new weapons were added to Modern Warfare 3 and Warzone with the Season 1 update which brings the XRK Stalker into the roster. But you need to unlock the sniper first and I can help you earn it in this guide.
How to Get the XRK Stalker in Warzone and MW3
To unlock the XRK Stalker, you need to earn at least 15 Battle Pass Tokens to complete sector A4 of the full map. Every new weapon that is added at the start of a COD season will be tied to the Battle Pass as free content, so that includes the RAM-7 and the Stormender as well. Luckily, you can choose which ones you earn first.