Check trade and go into order strategy and quality. If you have a >12 month low water mark change it to 12-24 months and place the order quantity at 36-48 months. You will spend a lot of money on supplies but will buy supplies much less often. You shouldn't have to worry about being low on supplies ever then.
I may have misunderstood the question though and I think you mean't that you aren't short on supplies but the supply index is below 100? I wouldn't know how to help with that.