Buy a zombie spawner from someone for cheap.
Stand in front of it with your cross-hair over the spawner, and type /mbox set blaze
*It costs a small amount of mt credits to change to a blaze spawner.
Enjoy your infinity blaze rods. <object class="emojione" data="
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(I have 3 of them now, and it's fun: Use a fire resistance potion and go kill them as they spawn until you have enough rods.)