Assessing or auditing all suppliers is not mandatory.
Let’s start, divide those 1000 suppliers into two types: those that supply products/services related with your company’s offer (for example, raw materials suppliers, subcontractors, …) and others.
Then, for the first group check if, for your company, it makes sense to establish a border based on amount purchased. So, focus your attention on those that your company work more.
Then, you can establish another filter, those that supply a customized product or service versus those that supply a standard product.
Then look into the result and check if it makes sense. You performed a risk analysis of your suppliers and you decided to focus attention and other resources on those that have bigger potential impact.
Amount purchased may be related with frequency/probability. Customized and incorporated in the offer may be related with severity of consequences.