CV, I don't know if you make it into the big smoke too often, but I got my mustard seeds in the little deli beside the jewellers at the back of the Westbury Mall - just off Grafton Street.

I actually got too many (bought 4 packets of 50g each and only needed 2 and a half). So if you want, I can post you down the 75g or so that I have spare when I get home tonight.