are you meaning the swingarm or linkage ?
The linkage uses torrington hk1812v which is avaiable at any bearing shop easily. Aprilia use metal seals but most bearing shops will have rubber versions which work just as well.
If you mean the swingarm it's a mixture of the above bearings and HK3026 which again is readilly avalable.
Just make sure they are open and not caged bearings they supply as you can get both.
use a waterproof grease when repacking or they will rust. White lithium or marine grease is good.
http://simplybearings.co.uk/shop/bearing_wizard_page1.php?gclid=CJTv-qK-h5cCFQ2IMAodIAir8Q
Update on that is the uncaged version is a protected part (aprilia patent) but several bearing shops have made them up by removing the cage and just adding more needles on the standard bearing. Just looked up the Aprilia price as well and it's not that bad.