Not sure if you went to the Cockle Banks from Scarb? I got my 50 pretty easy from there last week, again average size as they tend to be from there though. Out of interest I took a packet of Gulp sandworms and reckon it was 50/50 with the live worms. Certainly cheaper with the livies being around $30 each (slight exaggeration).
Out from Nundah I presume would be the old compass adjustment buoy area, buoy's not there anymore unless replaced in the years since I've been.