One suggestion is to use nothing but Plasti Dip (also known as tool dip). It is a chemically engineered rubber coating and therefore doesn't affect latex allergies. You can get colors that are pre made or you can buy a clear version and then add dyes to it (that usually comes with the clear version). Most people I know will use black as the base coats, then paint the weapon then seal it with the clear coating over top of it. My suggestion would be for 3-4 layers of the black (until you can't see the foam underneath the coloring) then two coats of the clear. And since you're only using one product for everything, it is easy to buy it all at once. If you can't find it, eBay it baby! You will want to use this in a ventilated garage or outside as the vapors are quite obnoxious.
Now, if you want latex, I would suggest Douglas and Sturgess in San Francisco, CA. They have something called "mask latex" which is a thicker version than the latex you get at makeup shops. It comes in quarts, gallon and 5 gallon pails. This stuff is great for casting in plaster molds as well as application with a brush - taking only about 4 coats to do a proper covering. Note that you'll probably need a new brush every 4 coats or so if you clean it well in between. It isn't as obnoxious as the plasti-dip however it does use ammonia as a base to keep it from drying out so if you put your head near, over or directly into the bucket, you'll get a blast of the ammonia. You can use any acrylic/water based paint to color it. I usually use 2 ounces of paint per gallon although you will want to test it out first for color since the latex comes 'white' which actually dries that yellowish color most prosthectics come in. Do realize that the latex will dry a darker color than what it looks like so, again, test it out. Best way to do that is to have a piece of plaster that you can dab the latex onto. This will help dry the latex quickly.
You can use the clear Plasti-dip over the latex afterwards but I usually just paint the whole thing with acrylic paints to cover the latex. Yes, the paint does wear off eventually but usually it is a quick fix. You can also color the latex to keep the color. For instance, I make all my weapons coated with black latex however when it comes to the wooden shafts, I mix up a batch of brown latex, usually with a bit more paint in it to make it more opaque. I then use a 'dirty' brush (one with a lot of latex clots on it) to brush it on. This results in the wood grain effect with the black bleeding through or being revealed partially in the strokes due to the clotting of the brush. Or you can use a clean brush and run a comb through the wet, brown latex but you have to be quick and decisive. Futzing over it will result in peeling away semi-dried clumps of latex.
Hope all of that helps!
Oh, on a designer note - whenever I latex pipe foam, I always strap it first with duct tape, leave it for the night then pull off the tape in the morning. This removes the protective coat that the foam has and helps the latex bond better to it.