Search for “alexa top 10 million” to download the list of top 1 million web sites ranked by alexa.com. Then you can find all pinterest sites from the list.
Alternatively, you can do DNS lookups for all pinterest domains by appending each TLD as suffix. Drop the ones that are reported as “Non-existing domain”. You’ll need to write a script to do this (or see if such a script is already available).
