For wood:
Try a search on ebay for "ironwood scales" and "stabilized burl".
You can spend a lot on a nice piece and try to outbid someone, or just bid on a piece that has no bids, and you are likely to get it. I hardly ever see more than one or two bids on knife scales on ebay. My wife just won a nice set of ironwood for only 9.99 plus shipping, she was the only one that bid. I've seen stabilized woods sell for a lot cheaper on ebay than on the knife supply sites, and you get to see what you are buying.
For attaching:
1) First, trace the outline of the tang onto the scales that are clamped together, and cut the scales slightly larger than the tang, so you don't have to work down as much material when you get to the shaping step.
2) **Clamp your scales together and FINISH the front part of the handles, because once everything is glued together, it is going to be hard to shape and finish the front part of the scales.**
3) Sand the tang of the knife with rough sand paper like 30 or 60 grit. And if you can use a flat screw driver or dremel to put scratches in it to help the epoxy hold, just don't get too close to the edges.
4) Use Devcon 2ton epoxy, or a similar slow curing high strength clear epoxy. Glue one scale on the one side and clamp with spring clamps. Don't clamp it down tight or you will squeaze out all the epoxy.
5) Once the first side is dry, if you want to use any of the pre-existing holes, or that oblong hole for a lanyard hole, then use the existing hole as a guide to drill through the scale that is already glued on.
6) Next glue the other side on the same way you did the first, and when it's dry, use the hole you drilled through the first piece as a guide to drill the second scale, if you are using any of the holes.
7) Now, use rasps, files, sandpaper to shape the rest of the handle. The front part should already be done, but now is the time to do the top, bottom, and back. This step takes the longest, and the most amount of sweat, but if you are patient and take your time, it will come out great.
Disclaimer: I have only completed one knife and am working on my second, so take my advice for what it's worth. This is information that I have come across, and this is how I did it for my first knife and it went well. This is the best way I know how to describe it, but maybe some more experienced makers will have better, or different advice for you.