Hi @castle, I don't know if they do ADA but you could always call or visit Scaped Nature in Norwich. A bit further away from you: @Aquarium Gardens (website) do ADA and also have ADA tanks along with tools etc. If you can't find what you want on their website, call them and see if they can get items in for you.
Update on AG, they are now actually selling Cube Gardens, give them a call I'm sure they will order what you need.i think AG might start stocking Cube Gardens soon. Drop them a line.