What is Glutaraldehyde and where can I find it?

Glutaraldehyde isn't a food additive, so it doesn't have an E-number registry entry; Glutaraldehyde simply shouldn't be in food! If food contains that aldehyde, it’s contaminated. Usually, food gets contaminated with Glutaraldehyde through migration from plastic packaging in contact with the food itself. But nobody checks for that! And there's no one coming to protect you there. So, I guess one way to avoid any chance of Glutaraldehyde contact is to just stay away from things like deli meats, cheeses, and similar items that are wrapped in plastic. Unfortunately, our E-number advisory service only covers food additives, so whether it's Glutaraldehyde used in cosmetics or food contamination via that compound, it falls outside the group of substances we actively deal with.
Then there's the issue with glutamates—those flavor enhancers. First off, the medical link between glutamates and Glutaraldehyde confuses me, because those two compounds have absolutely nothing to do with each other. It makes me doubt the quality of allergy testing. But, assuming you really are sensitive to glutamates, the best way to dodge them is to stick to as many fresh, whole foods as possible. I know that advice feels like a cliché, but it’s still smarter than the industrial assault of glutamates on our food supply. Fortunately, most foods containing glutamates are labeled with E-numbers ranging from E-620 to E-525. We're talking hot dogs, pâtés, processed meats, tons of sauces, various seasonings, deli slices, snacks, bouillon cubes, instant soups, mixed spice blends, ketchup, gummy candies, mustard, horseradish, mayo, even toothpaste, plus entire Chinese takeout menus, Japanese restaurants... There just isn't a foolproof recipe for pinpointing glutamates in products. Your only option is to trust the labels and avoid anything marked with those specific E-numbers.
Or, like I said before, just use some common sense and eat high-quality food.

Glutaraldehyde is used for sterilization in medicine and as a preservative, but NEVER in food products. It isn't on the list of food additives, nor is it marked with an E-number. Therefore, it isn't clear to us where this connection between allergic reactions and Glutaraldehyde in food comes from. Glutaraldehyde is "troublesome" and toxic, but it shouldn't be in food at all.
However, when you say you're reacting to snacks and similar products, that points toward a different kind of reaction. It's likely—and this isn't a rare case—a hypersensitivity to flavor enhancers like glutamates and guanylates, which are marked by E-numbers from E-620 to E-629. You should check their properties and usage on our pages under those specific E-numbers. They are found in massive quantities in the exact products you mentioned. It's well known that these flavor enhancers trigger allergic reactions and many other health issues. These are completely unnecessary additions to our diet; consuming them is a risk that is, frankly, civillizationally unacceptable.
Unfortunately, in your case, we're looking at glutamates, guanylates, or Glutaraldehyde; you'll need to go back and double-check the source of "your" misinformation.
E620 Glutamic acid
E621 Monosodium glutamate
E622 Monopotassium glutamate
E623 Calcium diglutamate
E624 Monoammonium glutamate
E625 Magnesium diglutamate