Here is a collection of all of the swapped Default Pickaxe paks I could make/find. (Essentially, free pickaxes for 3.5-8.30) If you have one that is not in the repository, dm me at Jeppy#3076.
Instructions: Download the .pak file in the folder of the pickaxe you want. Next, drag that .pak file into your FortniteGame\Content\Paks folder. Then, copy a .sig file and change the name to the exact name of the pak file but with .sig at the end instead of .pak. Then, Just load up Fortnite and you should be able to use it in game!
One exclusion: Currently, the Galaxy Pickaxe isn't working properly in FortMP or RiftMP, but works in singleplayer just fine. I will try my best to find a workaround, but I am not confident.