I think there is a next-generation HomePod coming — even if it's more of an Apple TV/HomePod combo, or something akin to a Home Hub. However, I also suspect that may be years away. After all, just look how long it took to get the second-gen Apple TV 4K. These products aren't a priority for Apple.
As for the original HomePod, if you're willing to go with a unit that's not new-in-box you might have some luck shopping around at local retailers that used to sell them. Stores that have display models are happily selling them off now, and if you think about it, a HomePod set up as a display unit mostly just sits there collecting dust, so many of them are probably still in pretty great condition.