John,
I met with my plastics company this morning and they are going to try to get a batch of chucks to me in the first part of January. They have been very backlogged, but they do such a good job that I hesitate to go somewhere else.
With regards to the two springs, I like to put the vessel on the plunger and have it supported above the rings until I'm ready to stomp it down. A closed segment vessel with 8-10 rings is heavy enough that putting it on the plunger will immediately cause it to plunge and probably before I'm ready for it to do so. The second spring is simply to keep it hovering over the rings until I'm ready.
This is completely optional, but I've found it to be beneficial. It won't make any difference to the gluing or clamping process, as you say.
Lloyd