Combining Multiple SKUs Into Single SKU. Only The One SKU Can Be Seen Online And Purchased

Shopify Apps
1

I need to be able to combine multiple SKUs into 1 SKU. Only the one main SKU can be seen online and purchased individually.

SKU A - Is the Item Sold which is made up of SKUs B, C, & D
SKUs B, C & D cannot be seen online or purchased on their own.

I need this for inventory tracking and eventually for 3rd party kitting / order fulfillment.

Any ideas on how to achieve this, even if an app is required?

Thanks in advance!