The bodyshell, part number UM18, is still listed as available to order from Kyosho Europe,
price is £18.10 
As an alternative there is a replica Turbo Ultima body available here
The rear axles use standard 12mm hex drives, so a lot of wheels are available from Tamiya, Academy and Kyosho that will fit on there.
The front axles are the tricky ones, with the axle being 4mm. For my Ultima I use HPI front wheel adapters that let me use 4 x 8mm wheel bearings with Tamiya front wheels that have an 11mm hole.
Alternatively to use 5mm axles get the uprights and axles from the Tower Hobbies ST-15
To fit Associated or Losi front wheels replace the front axles with Kyosho Ultima RB axles, part numbers RS26 front wheel shaft and RS3 knuckle arm, changes the axles to US size which means the wheels and US size bearings will fit straight on.
If you need any spare wishbones and Kyosho have no more, then take a look at the
Tower Hobbies ST-15 parts list as it uses identical wishbones and suspension mounts.
Shock clamps are very hard to come by and the correct ones are very expensive to buy. I use a set of shock clamps from a Kyosho Raider buggy. I picked up the complete buggy for less than the price of the Ultima shock rebuild kits, and the raider clamps are a much stronger design.