Wiktionary
vb. 1 (context idiomatic transitive English) To buy the whole of, the totality of something. 2 (context idiomatic transitive English) To buy whatever is available of something.
WordNet
Usage examples of "buy up".
Numbers of Arabian horses are collected here from the inland country, which the merchants buy up and carry to India, where they gain considerably by disposing of them.
This afternoon I want you quietly to buy up all the available guns in Honolulu.
One quiet success story is Preservation 2000, an ambitious program designed to buy up endangered lands and save them from development.
We'll get him a good agent, we'll buy up what he has on the market, using dummies-and keep them ourselves.
So long then as the poor man hath to sell, rich men bring out none, but rather buy up that which the poor bring, under pretence of seed corn or alteration of grain, although they bring none of their own, because one wheat often sown without change of seed will soon decay and be converted into darnel.
With the FOE money you began to buy up all the imports around Old North Australia, and when the government finally declared an emergency, you had secured final title to one and a half stroon years and to more megacredits, FOE money megacredits, than the Earth computers could handle.