Vendors need business just as badly as you do. They
can understand that you have no resources to pay old invoices. However if you're going to buy any new unit(s) then why shouldn't they be from that vendor? In fact you're doing them a favor not buying from someone new. They get to make that fresh margin.
Now the terms on which new material is shipped can vary greatly. But even the worst one is deposit and cash paid on delvery. Why not get deposits from your customers. It isn't the end of the world. And payment on delivery too. Give them a great discount!