It would certainly be helpful to know the pending orders for finished
product per month. With this advanced information, one could then
assume that the current inventory level, less the build quantity (minus
some percentage for fallout), and less the safety quantity would tell
you what was required to be ordered to maintain the safety level. There
are some vendors that will work with you to supply various quantities
when necessary to help maintain your safety level, but obviously, they
need to know projected production levels.
If you're looking for some formula or other help in resolving this
problem, please respond directly to my e-mail. The current problem
description is rather vague!