The regular Triumph shops in Bris have the usual mechanics, I've not heard of anyone that specialises in R3's.
I take mine to ProCycle Dyno for tuning and Fred is connected to a workshop, he might have a suggestion if you talk to him about power upgrades.
Ozrider (on this site) trades in Bris as LMS and has helped rocket riders out with performance exhausts.
I fitted: ramair filter, LMS headers, LMS crossover and triumph TORS before getting Fred to tune on the dyno. (194hp, 165tq)