Are there parts readily available for building a board using these switches from scratch?
Depends how “from scratch” you want to go. If you can order some laser-cut acrylic/wood or water-jet aluminum/steel (or have your own access to such machinery), you can make a plate that accepts Alps (and Matias) switches. Alternately, you can buy old Alps keyboards on eBay to swap switches into / harvest parts from for your own mods.
I’ve been CNC cutting case/plates out of wood, and plan to hand wire the switches, so the only parts needed are generic wire, solder, diodes, wood, and a microcontroller board (e.g. Teensy). That may be more “from scratch” than you’re looking to go though.
More conventionally... as mentioned, Matias is going to run a group buy for a 60% keyboard kit (including optional assembly). And there are some other upcoming commercial keyboard projects from various vendors using Matias switches. Sprit was going to have an Alps-compatible kit at some point, but I’m not sure if that’s happening yet
http://geekhack.org/index.php?topic=50580.0.
What exactly are you looking for? What kind of board do you want to build?