It'll take an investment in some specialized equipment (courtesy of eBay) but you can make your own View-Master reels.
View-Master cameras come in two varieties: Personal and Mark II. A 1952 Personal View-Master camera is pictured above.
You'll use your camera to shoot slides. Make sure when you have your film developed that you specify "do not mount," you'll want it returned to you in a continuous uncut strip, not mounted into individual slides.
In order to precisely cut your film into little TV-screen shaped chips suitable for View-Master reels you'll also need a View-Master Film Cutter. Keep your eye out on eBay for one of these.
Like the cameras, the film cutters also come in in two varieties, Personal and Mark II. Personal cameras and cutters expect stereo image pairs to be laid down in a horizontal format. Mark II equipment uses a diagonal format.
The two formats are not interoperable. Both your camera and cutter must be of the same type.
Once you've cut your film into chips, you'll need to insert those chips into blank View-Master Personal Reels.
These reels can be hard to come by now. The machine that used to manufacture them no longer exists, so they are out of production now, and the world supply of blank reels is becoming scarce. The last time I bought any, a few years ago, they were about a dollar each, but i noticed recently (7/4/2005) they were going on eBay for $4 and more per reel.
You must insert the film chips into small pockets on the side of each reel. Wear finger cots or gloves.
Sometimes the pockets are hard to open. You may not need a film inserter (see envelope above) but you should at least have a thin strip of metal useful for prying open pockets which may have sealed together with age.
The metal object in the picture above is not an original film inserter, but a more recently made device called a Spee-D Pocket Expanding Tool.
You can view them in a standard View-Master viewer, available at any toy store. You can even have your own reels mass-produced by Fisher-Price's custom orders department. Nowadays, with a deposit, they'll rent you a Stereo Realist camera.
Here's a place that contacted me recently by email. Nan Peng Stereoscopic Picture & Culture Transmission Company I have no further details than what is available on their web site.