If you're out west (Kingston) or east (Old St.) there is a Vietnamese supermarket that sells them (run by a friend), possibly cheaper than getting it posted
my sister lives in HCMC so I've just asked her if she can send me over one of the filter devices... looks simple brew method, maybe good for travelling/office (without condensed milk, with normal coffee)
If you're out west (Kingston) or east (Old St.) there is a Vietnamese supermarket that sells them (run by a friend), possibly cheaper than getting it posted