You can see all the Weapons and Mechs through the Inventory.
The Mechs and Weapons that you have not unlocked in the Progress Path are displayed in the Locked section when sorting by availability.
You can go to the Progress Path to check how much XP you need to unlock them.
You can also choose to sort Mechs by their Energy Capacity or whether they are in your Squad or not. Weapons can be sorted based on Energy Cost or whether they have been equipped or not.