Hi AdeleKaye & nduro
Have you had a look at DatapelSystems ? This is a very strong Inventory addon to MYOB and full WMS system that is used extensively by MYOB users with more complex inventory management needs.
Here is a link to their:
If your issue is more related to reporting over Inventory, sales and margins and other analytics then a number of the Advanced reporting MYOB addon solutions will be able to help there.
As an example our Busines Intelligence solution BI4Cloud will let you do extensive Sales & Margin reporting over any date range, by Customer, State, Salesperson, Brand, Suplier and of course down at Item and even transaction level. We also integrate to and report over Datapel WMS. Feel free to do a 14 day trial and see if this is of any help.