That’s where I get mine from.
How you use it: here’s the “latexing” from my (still in progress) how-to:
Latex is the rubbery stuff on the outside which protects it from damage and makes it look good. When you buy it, its a thick white gloppy fluid which dries clear (or maybe a bit yellowish - I’ve used it to make guts before). You’ll need to paint enough coats of latex on to get a smooth, coloured finish.
There are lots of different opinions on how many coats you need and what colours they should be. This is just what works for me.
Dilution: As mentioned above, latex is quite gloppy. You’ll need to thin it down a bit with water. How much depends on how gloppy your latex is, but you want something about the same consistency as milk. Too thick and you’ll obscure detail and it will take longer to dry (OTOH, thicker latex = more protection).
Colouring: Most people don’t want their weapons to look like foam encased in yellowish transparent rubber, so you’ll need to colour your latex. You can use ordinary acrylic paints for this, the ones you get in a tube from Whitcoulls (Reeves student brand). I use black for undercoats (largely so I can see where I’ve painted), and a variety of silvers, browns, coppers and golds for topcoats. How much to put in is a bit of an art, and varies by how much you’re colouring. For undercoat, I do about a half jam-jar of latex, about a Tbsp of water, and a few squirts of black paint, until it looks battleship grey when swirled (this gives quite a thick and coloured mix). For top coats, I’m typically mixing them in a tray, and its usually a squirt of paint to ~20ml of latex.
Space: Latex is messy, so you don’t to do this in your living room. It also takes a lot of time - a dozen or so coats, and 0.5 - 2 hours for each coat to dry depending on temperature and humidity - so you need somewhere you can get messy. I use a garage.
Brushes: I use disposable foam ones from the $2 shop, and go through a lot of them. The smaller brushes are best, the big ones can be trimmed to size and the offcuts used for doing handles or small weapons. I expect to get 2 coats of latex out of a brush before having to chuck it. try and get the latex on smooth, and try not to put so much on that it forms dribbles or bubbles.
Drying: Just like paint, you don’t want anything to touch your latex while it is drying. For small weapons (e.g. throwing knives, small daggers) you can prop them up in flower pots. For bigger things, you’re going to need to hang them from the ceiling. I tie a strip of cloth around the end I’m not painting, and use string and bulldog clips to hang it. For the ends of big weapons (e.g. handles, axe-heads) I either wedge them upright, or hang them off the edge of a bench (with something on the other end to stop them falling).
Undercoat: This is the basic protective coat. I use ~8 coats of black-tinted latex, which gives me a nice, gloss-black coating (which dulls over the next few days).
Top-coat: The coloured bit, usually 3-4 coats, colour depending on which bit you’re doing. For blades, I use silver mixed with black, increasing the amount of silver with each coat; to get a metallic look, you want it to go on a bit streaky. For blades that I want to look especially shiny, I switch from the usual Reeves student silver to Derivan metallic silver, and cut out the black. Gold can be done by similar methods. For wooden handles, I use a straight dark brown.
This gives fairly plain, blocky colours. As I said above, I’m not an artist. If you have a better technique to make things prettier, good on you.