For the big blocks consider making some by joining 2 two litre cartons or covering boxes you have. They will play with them uncovered too so just stuff empty cereal or cracker boxes with newspaper to make them less crushable. The thicker diaper wipes boxes are also great. Problem is storage of course. I know the blocks you are talking about and they do last a long time. Presume people have them and use them till they disintigrate and then recycle them vice sell them. You might try putting a wanted ad up for them and someone who is debating what to do with them might be inclined to sell them to you.