ALPS Microdry technology was indeed a half-decent way for a typical "home hobbyist" to produce small quantities of "proper" waterslide decals in white and metallics etc. The technology was used in a small number of printers by ALPS, OKI, Citizen and Kodak (possibly Roland too?). However it was an old technology intended for short run "proof prints" not everyday printing, and sadly ALPS have now stopped making any more Microdry printer hardware. Most of the models are only at their best/most flexible output when used with drivers on older operating systems (Windows 98).
Consumables will be around for a year or two yet (with steadily increasing prices no doubt), but then that's it until someone else comes up with an alternative in the same "home user" price range.
The printers *were* cheap on eBay but have been creeping up over the past 2-3 years. Trouble is they're not particularly robust and the heads are prone to burn-out over time, so buying a used one can be a bit of a risk.
Yes, I did buy one specifically to make my own decals - this was a few years ago when they considered them to be affordable and I had a specific project in mind that needed white decals. Even then it was something like £70 second-hand on eBay! Suffice to say it and it's dwindling supply of cartridges are jealously guarded, as is the old Windows 98 system I run it on!
Must admit I've yet to be totally convinced by the various inkjet / laser decal kits and techniques that rely on "inverse" printing the background colours onto white media in order to achieve white decals.