The Scouting 2008 50¢ is a collector coin, and won't be going into circulation, so each one will cost $4.95 in Australia.
RE the Scouting 2008 $1, this is straight from the Scout website:http://www.scouts.com.au/main.asp?iMenuID=11624150
"Centenary Coins - In late February, there will be launched: a $1 circulatory coin; and three Centenary commemorative coins ($10 gold, $5 Silver and $0.50 Cupernickel)."
Once they are released for circulation, you should be able to get as many as you need for face value, plus postage costs to US. If anyone can get a Security Roll for you there will be 20 coins in it.