The Monsoon used to have a solid keel bulb made out of, I think, cast iron. Not anywhere near heavy enough. It did need replacing.
The lead shot and epoxy resin filling of a plastic bulb is quite standard. and for 1.2kg of postage, I can see why companies don't want to do it.
You can buy keel bulbs, plastic pods, from other model suppliers, as long as they will take at least 1.2kg you should be ok.
Lead shot may be banned in some countries for fishing or shotguns, but they are still available. As are lead-substitute shot, which are almost as heavy I think.
If the bulb is split, but not too deformed, you could just use masking tape to hold it together and fill with epoxy and shot first, before attempting any repair. If it has fallen in two, then I would scour the inside surfaces first to give the epoxy something to bite on.
just my 2 cents.