See Photolytic’s post here http://www.cdags.org/dagforum/topic.php?id=140#post-2534 for a link to buy the plater’s tape in the US. It also gets used in circuit board manufacture, so do a web-search for circuitboard plating tape or some such. I have seen masking lacquer for sale at jewelry or electroplating supply houses. For example, in the US these are Caswell, RioGrande, as well as my local which carries Grobet products.