I don't mean any offense, but I feel as though you might be taking the name of the product literally. You might be looking for a faux bone finish - but that stuff looks like a sort of...Friendly Plastic or sheet styrene-esque material that can be carved, sanded, melted, what have you. This material you've linked to doesn't seem to have a texture of its own - so you'd have to add that with some sort of sculpting medium - so while a it might prove useful to create your initial shape, you'd still have work to do to get things where you'd need them to be with regard to texture and detail. Additionally, the sheets max out at eight inches by eight inches, so they're much too small for the blade (unless there's a way to join them - which maybe could be accomplished via melting). Having used reference photos (including head-to-toe shots of Ackles increased to life-size in Photoshop, then cross-referenced with shots of him holding the blade), I arrived at a length of eighteen inches, so you'd have to join at least a couple of these together in a way that would make them strong.
Having no understanding of how to work with the material, I think it might be the smarter play to use materials that are familiar to you - but if you've got the funds to buy some and experiment, and you're feeling adventurous - give it a try.
My build is Super Sculpey over a 3/4 inch wooden template. I carved into the wood on a bench grinder, with rasps, and finally with a Dremel tool - then I used Sculpey to contour and shape with more control. Texture was created using Liquid Sculpey and a succession of sponge brushes. These things are easily obtained and super easy to work with - and cost me less than the material you're investigating.
Don't know if that helps at all, but good luck!
