Walther makes the P22 which is similar looking to the P99. It is scaled down in size and is about 1/3rd or 1/4 smaller than the P99s. Look in the Walther section on this site and you can read a lot about it.
Here are some links to see what it looks like and its features:
The GSP rifle is a kit requiring the GSP pistol.
The kit itself is $1000-$1400 USD. There is a complete rifle with pistol, carry case, scope, etc., for $6500.00 USD.
10 round magazines are $125.00. http://www.carlwalther.com/gsp_rifle.htm