The problem with 30-round L4A1 mags here in the States is that since there aren't many L4 Bren guns floating around the only people with an interest in these are L1A1 & FAL shooters. Most L1A1s here are built with Imbel metric receivers, so magazines with the Commonweath pattern front lug won't fit. DS Arms out of California contributed to the problem by buying large stocks of L4A1 magazines and 'converting' them to work in metric receivers by removing the front lug and punching the 'V' shaped FN-style front lip in them. From what I've been told by several owners of these butchered mags, they don't feed reliably in metric or inch pattern rifles. DSA claimed these were a stop-gap until their new production 30 and 40-round mags were available, but last I heard (4-6 months ago) they were several years behind schedule and no release date was in sight.

As far as the original subject of the post, I think it's telling that, even given their relative scarcity, these mags have been getting relisted on GB for about a year now without selling.