I'm sure Nic (aka Pinkspoons) will be able to tell you more detail however I can tell you a couple of things - the smaller uncased gulvvases were outsourced by Holmegaard to a British company called Cascade and are generally much cheaper to buy than the opal cased gulvvases which fetch significantly higher prices.
There are lots of modern foreign copies floating around the market - so do your homework - check the size and overall dimensions, look at the shape closely and, if in doubt, don't buy or even better put a link here to the item you're interested in and get the member's opinions before you part with any money.