Does anyone know if there is a "Stock by Attributes" version that actually works with Zenvcart 1.5.3 ?

Curiously why zen developers have created an attribute except NOT included the important aspect of the product attributes (see below)?

Why can't we do this?

Item code=test01 Item attribute 'Large' / 'Red' = Qty = 10
Item code=test01 Item attribute 'Medium' / 'Red' = Qty = 5
Item code=test01 Item attribute 'Small' / 'Red' = Qty = 8