Oops, was gonna reply to this but went offline.
Anyway, as far as steel H or I section rods go, youll have to get some made up for roughly 600 quid +VAT. Cams are available but not a very large selection and nothing really that wild due to the chillcast, hollow blanks they use, not everybody can get their hands on them. Piston, whats wrong with the OE ones, swap to forged items and itll provide no power gain but run rougher when cold. Throttle bodies, if your looking for a kit youll have to wait, but the manifold is available for DCOE flange bodies which cost about 150+ for the bare bodies so you can build up you own system no problem, injectors, also available at higher flow rates, but if you swap to throttle bodies you wont be limited to the OE ones and lucas/bosche are the normal choice.
you got the money then you can buy the parts.