Hasegawa has a "Voyager" model, and there is the old Lindberg "Vanguard Satellite" model. I've found these listed for sale.
Generally, spaceprobe models are rare and limited production. If you can do paper models, there are quite a few of those floating about. Otherwise, your best bet is to cruise the auction sites like Ebay.
Good luck!
Gary
PS> You might check here.
http://www.collectspace.com/