First off, where are you located?
If you are refering to the blue cloth Home Service helmet :
Rounded peak or pointed?
If you want to start buliding one up from scratch you can get a repro from http://www.ushist.com
They sell an Indian wars replica dress helmet for around $60, also chinchains , but I think they might be short ones (not the full drape around).
Finding the hardware is the next challenge.. The chinchains are available from a company who produces parts for ceremonial helmets.....they also have spikes etc... http://linkorient.trustpass.alibaba.com ... elmet.html
I am told there is a dealer in the UK called Peter Green who can supply cruciform bases etc, have not found contact info for him yet. Might be the fella who supplied the Thin Red Line webstore, not sure. If you get contact info, pass it back this way =)
I have found a replica helmet on Alibaba.com made in Vietnam, cant locate it right now. Search around in there, not saying this is true, but I would not be surprised if the one discussed above comes from Vietnam or India. If I find any more info I will post it.