Looking for a help with a complex vertical and horizontal lookup... (complex to me!)

Morning folks, I've got the following complex issue:

...................Trader1 Trader 2 Trader 3 Trader 4 Trader5... Trader20 (Horizontal)
Commodity1 .....0.....2.....0.....1.....1
Commodity2 .....0.....4.....0.....-3.....0
Commodity3 .....1.....0.....0.....5.....0
Commodity4 .....0.....0.....2.....0.....0
.
.
.
Commodity 36 .....2.....1.....1.....0.....0


I have 5 cells that are basically a drop down list of all the traders, so the user can select up to 5 traders.

Once the user selects up to 5 traders (lets say Trader 1, 3 and 5 for our example) I have the following requirements to fulfill:

Displaying all commodities that have non-zero, non-negative values associated with those traders in a list somewhere. For our example, this would then display:
Commodity 3
Commodity 4
Commodity 1

I have attached the example.

There are two asks:

The first being how to generate that list of dynamic results based on a cross-reference.

The second, is me wondering if it is possible to have a drop down-list that I can select multiple values from.

Both are clearly identified in the example excel file attached. Thanks a ton!

This works but only lists the first "Com" encountered. I was wondering how I can list all the Commodities that return a non-zero non-negative value. Re-attached sheet with your recommendation.