Inventory management is a precise art that has a large effect on a warehousing company's cash flow. Most suppliers tend to stock just enough raw goods to cover what they typically sell in a month. Since inventory management can achieve significant savings, many suppliers subscribe to lean techniques, which optimize this matching of stock requirements to sales as closely as possible.
If you are not on a supplier's list of buyers, you might not be able to access the 30-day supply because the company has not accounted for your order. Most companies stock an overflow for these kinds of eventualities, but not all do.
That is why it is important to question the particular supplier on what exactly is meant by a 30-day stocking of goods inventory.