So the step you are actually getting stuck on is filtering your recordset to return multiple results. Normally you could use DataAssist Search to do this, but that isn't working because you have a DB2 database.
So... hate to say it, but in some cases you need to write a little code.
You need to create a where clause from the submitted fields so you can filter your recordset. Once your recordset is filtered you would probably loop through that recordset and have to loop back through the form to get the corresponding quantity and most likely store the values in an array.
Then you can loop through that array and add items to the cart. This will require some knowledge of SQL and ASP scripting to pull off.