What should I do to fulfill a vow to slaughter a sheep and distribute it if I am unable to do so due to financial circumstances?

If the one making the vow anticipates his affairs becoming easier in the future, then the vow remains a debt upon him, to be fulfilled whenever he is able, unless he specified a time for it. If he becomes completely unable to fulfill it, then an expiation for breaking an oath (kaffarat yamin) becomes obligatory upon him.