Longfeather
Not a question that the .470 will be much more readily available in regards to ammo. For what you stated you will use the rifle for, I would choose the .470. However, having already been there I would get a .500, but that is just me. On my experiece there is really no significant difference in recoil and you pick up around 700 ft.lbs more energy at the muzzle.

As to reloading supplies, I recently purchased a set of RCBS dies from a firm out of Idaho. I will check to see if I can find the info, but all I did was a search on the net and found them fairly quickly. As to reloading supplies, MIDWAY has quite a bit on their web site for various calibers. SUPERIOR out of Sturgis,South Dakota.. will reload and regulate ammo to your double as well.

Good luck.
Ripp