Pet food can be bought from Feso Shop. If you don't know where it is, go to your toolbar (Alt+U), click/hover on the treasure chest icon in the left side.
Composite steel and cast iront can drop in certain field maps like Viron forests, but you can also exchange for them through an NPC.
Talk to Smith the Blacksmith in Reboldoeux Shopping street (he's near MM). You'll see there what you need to farm for each material (Bulk Coal, Steel Piece, etc.)