Geez people...the HPI rally is on the shelf at Hobby People.
It's still current on the HPI website, it uses 99% of the same parts from every other RS4 car (200mm nitro arms, axles, uprights, shock towers, pins, bulkheads, diffs, etc, etc...).
I bet you'll find more parts for it on a hook at your LHS than you will parts for the Pro 4.
I just got one that had beeen sitting on the shelf at another store for a couple years...$100 brand new.
It kicks arse.
I tore down my old Sport/Pro 2 and used all the good stuff to trick out the Rally. I got some shiny CVD bones, some purple stuff and rubber-sealed bearings...