Reddit reviews Lineco Neutral pH Adhesive, Acid-Free Dries Clear and Quick PVA Formula Preservation Material Water Soluble Flexible, 4 Ounces, Book Binding and Other Paper Projects, White

Yes. You buy it as solid polyvinyl acetate beads, and dissolve it in the acetone. You can have a very liquidy mix to get it to soak in (about as viscous as water), or a thicker mix that you can kind of paste on the surface. You can apply more acetone to loosen things up if necessary.

I don't think it's available pre-mixed. A) it's simpler to ship it separately, and B) you can control how thick it is.

As I mentioned, breathing acetone isn't healthy. Don't fool with it in an enclosed space. Some people are more casual with it, but I always use it in a fume hood, which isn't exactly common household equipment. Outdoors might be okay, but I'd still be careful. It's not something that is filtered out by regular filter masks because it's a vapour. It's also flammable. If you've not worked with hazardous materials, I don't recommend that route. Go for the water-soluble glue and just be patient with it. It will harden up eventually. Like I mentioned, the salt water might be a problem for your specimens, in which case you'll have to experiment to see what happens.

I use this stuff made by Lineco, which is quite watery to begin with. The 8-oz bottles are probably most convenient, and usually they're pretty cheap (<$10). Amazon's prices seem ... utterly ridiculous. Shop around. The Lineco glue is often available at art supply stores if you have one of those nearby.

Both techniques take some practice. Try something unimportant first.