Would be great to get a bit more context on what are our core interests and the vendor's core interests (most important), as well as info on bargaining power between the parties and what is the nature of the loss that the vendor incurred (is it one off or substained?)
A few high level tactics come to mind in any event
1. Improve your own negotiating position by finding alternative suppliers - you can find an alternate dedicated supplier, or split the volume between several suppliers and have them compete against each other to produce better terms
2. Restructure the terms to align closer to each party's interests: include a term that pays the vendor for additional inventory holding costs in times of delay, but exclude the vendor from being able to lift up prices in general.
3. Restructure services and your own operations: remove your own pick up operations and use the savings to have the supplier deliver to your own premises instead.
Hope that is helpful!