Extension to reduce 'option' stock for each item

I'm looking for a specific extension which I am guessing exists but I can't find it. Here's the deal: I have several items in my store which are "combos" meaning that they are comprised of other items which are sold individually. Here's the problem....when someone buys one of these combos, it doesn't reduce the stock of the individual item so I constantly have to recount the stock status of these items. It would be nice to be able to set in the option settings which items to reduce the count on when that single combo item is sold. Does anyone know if something like this exists?

Thanks!
Garret