Sigma is listed "for display only", ditto for the Ride Armor.
UPDATE: According to our good friend BCDirect (who wanders the showroom floor right this moment), the Ride Armor is said to go on sale. Pending further confirmation, however, you probably shouldn't start doing cartwheels just yet.
UPDATE 2: Courtesy of Toy World Order and BCDirect, we've got a some great hi-res photos of Sigma, Black Zero, and the Rider Armor. Check 'em, out after the break!
Stay tuned for more updates...
Sources: Tamashii Nations, Toy World Order