One of the more interesting ideas (and also impractical) are the "mini-syrups" that are used in the multi-beverage dispensers with the touch screen at places like Movie Theaters. Good luck getting hold of those. I briefly had a line on getting them from a local AMC because I knew the manager who wasn't averse to re-selling them to me at cost but she changed jobs when the pandemic made theaters non-viable. The existing Coke branded dispensers are so loaded up with various DRM/telemetry that even if you can get one at auction (which you normally can't since they are leased, not sold) it would be quite the reverse engineering process to get it to work "disconnected" from the Coke network.
[1] Funny story about how I spent four months trying to buy Diet Dr. Pepper syrup at the "restaurant" rate (which was about 1/4th the "retail" rate) elided.
In practice if you wanted some kind of home setup, you'd be much better off just buying the normal box of syrup like they use in fast-food restaurants, gas stations, etc.