finding job lots for things like macbooks or pc's in general that are woth buying to resell are difficult to find. Most have an awareness for their stock and will take out the ones that are worth selling indivdually.
but staking ebay and other online marketplaces is really the best solution.
I used to send old pc's to a company that recycled them and either fixed up, recycled the parts or got the machines to working order and sold them on to different markets or charities.