With festivizer the atmosphere of the holiday is always in your inventory. TF2 Festivizer is a tool item that players can use for one time only, and it allows players to decorate a select few weapons festively. Festivizer TF2 can be obtained only through unboxing via the crates. Or, you can find it for the lowest price on this page.
On DMarket, you can also trade tf2 skins and get items that you really need.