Ducky used reduced-force Xiang Min KSB-C (clicky, green) and KSB-N (linear, black) in their "XM" 1000-series keyboards.
Xiang Min KSB series switches are
Alps clones, i.e. they're not made by Alps or for Alps, but they're fully interchangeable with genuine Alps switches.
Alps switches have not been made since early 2012, when the Forward Electronics switch production line closed. (Strictly speaking, Alps's involvement stopped several years before that when Forward lost their licence to the Alps branding, but Forward Electronics continued production for a few more years with unbranded switches, as you find in the Matias Tactile Pro 2 and 3.)
You can buy Xiang Min KSB-C and KSB-N switches (not sure if Ducky spec) from Mechanical Keyboards, though if you want clicky switches you're better off buying
Matias switches. Note that Xiang Min were never consistent with the colours — the Tactile Pro 3 uses KSB-LE switches that are also green, and my sample KSB-C switches are ivory. Their colours are a bit random — stick to the product codes.
"
Green Alps" specifically refers to
Alps SKCL Green, a highly-regarded linear switch from Alps Electric that was discontinued by 1994.
In terms of keyboards with the same or comparable switches, your choices are very slim, and the Matias Tactile Pro (and related products) is the only one I'd be comfortable recommending. Hopefully as time passes, more products will take on the Matias switches. There's also the AZiO Levetron Clicker series (and various other rebrands) — no idea on reliability. That uses a similar Alps clone series.
