Substitute for calcium oxide (lime) to keep pumpkin from falling apart
Your problem is that you're looking for the wrong kind of lime.

Calcium oxide, or Quicklime, is indeed only used for building and chemical purposes.  You want Calcium Hydroxide, otherwise known as Pickling Lime.  You can but it online, or from any store that sells pickling supplies.

And it's a good thing you didn't try the calcium oxide, there's a good chance you'd have blown up the stew.  It heats up when hydrated.