Replacing a stock set of Alps keycaps requires a lot of creativity, perseverance, finances, luck, and irreverence for historical items. It's not uncommon to poach keycaps from several perfectly working vintage computers, leaving dismembered carcasses to be bemoaned by vintage computing collectors. There have been attempts, both commercial and DIY, to bring Cherry keycaps over to ALPS, but they have been less than ideal.
I came across an interesting MX keycap set which, if nothing else, offers at least another choice. The Skyloong keycap set is made of silicone and ABS with a profile similar to SA switches.
The most interesting part is its two-piece keycap: an ABS insert that snaps onto the stem and also into the silicone cap. It’s not unlike the two-piece keycaps found on Model M keyboards.