Don't think the X-Pro has been withdrawn... but I agree you can't seem to buy it in the UK atm...
However if you already have the conversion kit you could use that with a Madrat. You'd have to up-grade the shocks and turnbuckles a little but apart from that the cars are virtually the same.
If you still want a pro chassis to start with then you'd probably be best ordering up a
SX10 2w from TQ.
J