Inventory Planning - Only Suggest Manufacture Amount Based on Material Supply

My ultimate goal is to have MRP tell me how much of an item I can manufacture based on the materials I have in stock.

Example: We purchase potatoes in bulk (it has a stock item of Potato Variety - Bulk)

We sell that potato in 3 different sizes via manufacturing

Potato Variety - Size A

Potato Variety - Size B
Potato Variety - Size C

I want MRP to tell me how many of each size I can make not just based on SO but based on the supply of the bulk potato when the sales date of all of the above sizes (first come first served).

I thought turning off MRP for the bulk items would help with this but it still seems to be only looking at total sales and not the supply to make the sizes.

Thanks!