I've not heard of SS being specified as Half-Hard but from the description I presume you are looking for springiness as a characteristic feature.
Nowhere near the size you mention but I have a more than ample supply of 'flat' SS spring wire. It is 2.5mm wide and 0.7mm thick with rounded edges, I have lost the Certificate of Conformity that gave its metalurgical content but you are welcome to have some if you could use it, it might mean changing your design but several strips could be fixed side by side etc.
Ian P