The 8mm Mauser,  came into existence in 1905 when the 7.92x57J was upgraded with a 154 grain spitzer bullet with a diameter of .323. This was the primary military round for Germany during WWI and WWII.

Ballistics - Very similar to 30.06.

New Production Ammo can be found manufactured by Norma, Sellier Bellot ,  Winchester, and Remington to name a few.

Surplus Ammo - Found all over the place. Almost all corrosive. Make sure you follow corrosive ammo cleaning guidelines or you will corrode you rifle bore. Brass is pretty much unloadable.

Reloading Dies are made by Dillon Precision, RCBS, Redding, and Lee Precision , to name a few.

Reloading components can be found at Huntington's, Midway USA, and the Wholesale Hunter, to name a few.

Brass -  I suggest purchasing new  brass from Midway USA or other supplier listed above. Widely available and inexpensive.

Powder - IMR 3031 or IMR 4064 are both good powders for this round.