Weapons cannot be "leveled up" in TF2
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Strange weapons are obtained from unboxable crates.
No you cannot trade weapons for beta tf2 to normal tf2. Beta Tf2 is considered to be a completely different game by steam. Therefore the two game's inventories are not compatible.
download them from garrysmod.org
You can either play a lot and hope you get lucky. Or you can craft extra dropped weapons into hats.
You must play Multiplayer and get experience to "Level Up" and after a certain amount of level ups you can unlock new weapons for kits.