When you start modifying your bike beyond stock.....you need to keep track of what you have done so you know what to order when you need to fix something.  I have a page of notes for what all the non-stock parts are on my bike....and that way I can figure out what I need to replace anything that breaks.

You can order sprockets from any local bike shop, or any internet supplier.  Bike Bandit, Motorcycle Superstore, Ron Ayers, etc.

The tech section has a thread on the chain conversion.  It says you need to order:  "front and rear sprockets for a Suzuki 1980 GS550 with CAST wheel".

Here is the link to the thread if you need more information:
http://suzukisavage.com/cgi-bin/YaBB.pl?board=tech;action=display;num=1174239333

It is also stated in that thread that you can use a JTF 513 sprocket for a #530 chain...which can be accessed here:
http://www.jtsprockets.com/catalogue/sprocket/JTF513

Be sure the sprocket you order matches the chain pitch that you are using.