The receiving docks tend to consider them a nusiance, unless they use a shop vac to suck them flat. There may very well be a manager that wants to recycle them, but the schedule never makes time for dealing with the bags.

If you were to arrange picking them up from docks, plan on showing up on a daily basis if you aren't paying for them. If you slip the receiver a few bucks per bag, he should be happy to save them for you. Don't expect a receipt, that money isn't going to the company.

They are used in shipping containers, railcars, semi-trailers, etc.

I would not consider them for lifting a building or slab jacking, though they may be perfectly adequate.

That is good news. If you come across any addresses, names, phone numbers, web sites, manufacturing sites or GPS locations, send them along.  I'm in the Midwest and the trains don't stop till they get to Canada.