I purchased this product at Michaels craft store; I do not know how wide a geographic area their stores may be found, but there are a number of stores in the northwest states. I have seen similar products at Tap Plastics and at one hobby store, although I have not checked on the brand names of their products. Generally, this is a product used widely by ceramics hobbyists, and is used to create flexible rubber molds by brushing a number of layers onto objects which the hobbyist wishes to duplicate with any of a variety of casting materials. Therefore, it should be readily found, by whatever brand name, at any store which caters to either the ceramics or plastics hobbyist who wishes to create casting molds of existing objects.
I use this material to mask my models for painting. Although I have tried several other liquid masking products sold specifically to modelers for masking models, I have come to prefer this product for several reasons. It is quite inexpensive in comparison to any other liquid mask, it does not tend to become harder to remove when left in place for extended periods, it does not leave any residue, it can be removed even when not fully cured (the "wet" remnants simply dry quickly and may be peeled off), it is easy to "correct" if applied past the desired mask line, it stays in place quite well including allowing polishing of surrounding bare metal finishes when panelizing, and it peels of easily when the time comes to remove it.
Although I use hobby tape, drafting tape, Post-It Notes, Para-Film, paper, foil, and sticky-wrap as well, I estimate I use this liquid latex for about 80% of my masking, including panelizing, canopies, gear wells, and to edge rough-cut Post-It Notes or other masking materials used to protect large areas.
I use a chisel blade in my hobby knife to cut a toothpick to a wedge on the end, and apply the liquid mask with the wedged end of the toothpick. It flows well to either raised or engraved panel lines with out being too runny, and it is easy to freehand camo paint schemes which have a crisp demarkation line. If the mask flows over the desired line, I let it cure, then gently push the edge back to the proper place with the wedged toothpick. I use it over Testors Buffing Metalizer with no problems, and use it to mask the panels for different shades of Metalizer, buffing each out before applying the mask for the next shade. The mask stays in place so long as I don't get heavy handed with the buffing.
I do not use acrylic paints, so I do not know how this water based mask would work with acrylics for models. However, when the latex base is cured, I suspect that the acrylics would not affect it. There is one "downside" of using this product for masking. Paints such as Buffing Metalizer or other enamels do not readily stick to this material, so when it is removed, there is a tendancy for the paint "overspray" to not come away cleanly with the masking material. Often, there will be flaked remnants of the overspray which I must remove to obtain a clean line where masked. Again, the wedged toothpick comes in handy; I gently run it along the demarkation line and flick the "overspray" chips off.
I've tried many different masking methods over many years (I started modeling about 1951 -- does that date me or what!) and this liquid latex works as well or better for masking than any other product I have tried.