If you just want basic brown or blue you can look at Hobby Lobby if you have one near by and sometimes Joannes.
If you want a larger selection of colors I like http://www.suncatchereyes.net/index.html.
Size wise: most people go with 15mm or 18mm, though I think some went with slightly larger 20mm to give the poppet an anime like look.
As for the nose the pattern talks about using clay, but I like to glue a pony bead to the inside of the nose to help it keeps its shape.
Also I was told that if you put a pencil into the body and up into the neck it will help with the tipping neck syndrome many poppets get from their hair being too heavy.
Hmm, well let me know if you have any more questions and maybe I can help you out.