No one presently makes 126 film, but you may find some old stock on ebay or other sites - though it may be too old to give good results.
It is basically 35mm film that is not perforated. Instead, it has an indexing hole for every frame, and this hole tells the camera when to stop.
You can load 35mm in the 126 cartridge, but the perforations might stop the advance too soon, causing overlapping exposures. You can modify the camera, though you may have to work out how much to wind it (depending on the camera). You also either have to use backing paper, or tape over the window in the cartridge.
Some microfilms are not perforated, but are black and white. Occasionally you can find bulk rolls of unperforated color 35mm film. I found some color at Photo Warehouse a few years ago. They are an APUG sponsor, you can find their link at the bottom of APUG pages.
Any place that develops 35mm can do it for you (so long as they do color or B&W, depending on what you use), or you can develop it yourself. You might have to ask the lab how to deliver it to them (can they handle a 126 cartridge? Plus, they may not return the cartridge.)
To reload the cartridge is also a bit of work, but can be done. A few of us here have done it.
You can search the site for more information, but here are a couple quick links to get you started:
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