Slag glass was made by the manufacturer.
Some or all of the swirl glass could have been bought from other sources. Pretty sure they'd mix up the transparent separately -- maybe with their own mix or maybe from other sources, and then they could add the crushed cold cream bottles into that.
Cullet could be used on both ends at a marble factory. They could use it to make marbles. And they could create their own cullet in the process.
Vitrolite was a company which made glass products, and their cullet went to places like the Heaton swirl company. So Heaton could put Vitrolite cullet into their furnace and makes some swirls and then could have spilled some of the their molten glass or let marbles get stuck together in clumps, and that's how you get Heaton cullet.
If you see Akro cullet, that's rejected glass at the end of the Akro marble making process.