This is information that I have gained from the internet and from suppliers, so I cannot guarantee its accuracy.
Available from The Racing Line and estimated to give ~280bhp.
Milltek cat-back available from The Racing Line and estimated to give ~20bhp, TRL (The Racing Line) also do a Scorpion de-cat pipe.
The K&N panel filter part number 33-2392 should fit. HKS Super Hybrid Panel Filter SR012005 (70017-AM007) definitely does.
EBC pads appear to be the same parts as for the Evo 2/3/4/5
EBC USR1384
See this post for when I had the EBC discs and Yellowstuff pads fitted.
Apparently Eibach are now doing their Prokit for the Lancer, not sure if it is also for the Ralliart. Part number 6050.140.
ProKit Technical InfoFront and rear indicators are both the large wedge shape bulbs PY21W. Silvatecs look good on the Lancer.
Aluminium deal-pedal cover, part number MZ525044EX available from US and Canadian Mitsubishi dealers, not sure whether this can also be got in the UK.