You may try to contact the Samsung customer service center in your region, or local retailers. Unfortunately, I don't know the distribution of the SWA-4100, or where it's available.
I have been searching the Net for the wireless module and speakers for the HT-Z320 Home Cinema System. The user manual shows this module to be SWA-4100 but I have been unable to find a stockist of this in th UK. I read since that it is not yet available here. Are there plans to sell it here or is it indeed already here, somewhere?