If you search for "Devcon" or "plastic welder," you'll find plenty of places where you can buy methyl methacrylate adhesive for about the same price as a tube of epoxy - if you are in America. For Canadians such as myself, absurd markups and/or high shipping prices are the norm.
That isn't to say that you can't find MMA at a reasonable price up here - as I just found out, Home Hardware carries a "plastic epoxy adhesive," which can be found here. You can find the MDS here (links on page will download a PDF). Note the words METHYL METHACRYLATE in the section composition/information on ingredients. I've ordered a tube, tested it, and found that it set hard. Yes, this is the stuff we're looking for. Interestingly, the model number given on the home hardware page is 84125, whereas Permatex has information for items numbers 84145 and 84115 - probably because 84125 is the model number for a single tube (cream colour) and the other model number are for packs of 12.
Most stores don't have it in stock but will order it in if asked. Just be sure to have the product code to hand: 8698046. Also note that the packaging is labelled Permapoxy even though the company that makes it is Permatex. You might be better off ordering a tube in than finding a store that has them on the shelves, as MMA has a short shelf life.
The above won't be much help for Nerfers looking for Devcon in the rest of the world, but I can offer some advice: search for "plastic wielder" or "plastic bonder" rather than the brand-specific "Devcon" and don't forget to check whether your local hardware stores can order it in as well as searching local shelves/amazon/ebay/etc.