They were purchased through McMaster-Carr
All of the info is on the April 2nd coversion page; the shopping list is correct except for 2 things:
1. We used 6 (not 4) of the adjustable rectangular flanges (part 4936T64)
2. We ordered way too much of the galvanized steel pipe. 3 Pieces of 21' should be enough. We'll use the letovers to make the ladder.
Total cost of materials was about $2k...which may or may not be a shocker/deal breaker!