Vendors sell them and early fights don't really so much require them. I stock-up on them while I can and always end up with 2-3 full stacks of them by act 3. You can also craft them.
@@89qwyg9yqa34t I cant see your other comment, but its DRS stacking (damage rider source). They patched many of these out when they launched honour mode. I dunno how long these will be here, but its nice while its here.