30 Gibbs brass may be hard to find, but there are a few ways to make suitable brass. One is the false shoulder method, which is an expanded neck above 30 cal and then partial resized to 30 cal that allows for a tight fit into your chamber. Load with a standard 30-06 load data and fire form.
Another way is to use standard unfired 30-06 or 280 brass with the bullet seated out to tightly engage the rifling. Typically, for my old 270 Gibbs, I would apply a crimp to bullet to help prevent the case from moving forward under the firing pin strike. I and others have had decent success using this method, but I went to using 280 brass with a partial neck size to 270.
If you use the long seated bullet method for fire forming, I would recommend 280 brass resized to 30 cal, for standard 30-06 brass is a little short in he neck after the fire forming process.
For dies to load your new formed brass, you can use a 300WM neck sizer or Lee collet die and usually, the standard 30-06 Bullet Seater will suffice. Once the brass becomes too tight to chamber easily, you can simply discard the brass for new fire formed. Depending on load, chamber etc, you should get about 3-4 loads from each new brass before the body becomes too tight. If desired, you can then buy a 30 Gibbs resizing die, but brass is rather cheap and plentiful to make new cases.