Can heartily recommend Dean at Pipecraft in Basildon for help with exhausts, either in full or part.
The exhaust on my 14 year old RX300 had clearly been patched and welded over the years before we got it, and also was found to have a leak from an O ring too. Even part of the system was well north of £300 plus vat, delivery and fitting and this didn't include the front flexi pipe etc etc etc. Delivery was 7-10 days minimum at best, and none of the normal exhaust shops could help.
Dean spent time assessing what could be retained (not much) and what they could custom make, identified the O ring leak, and £240 plus £13.93 for the O ring later (supplied in 2 days by Lexus Rayleigh who were really helpful) I now have a silky sounding RX again!
Obviously his expertise isn't limited to the RX, he is able to custom make most things (and sounds!) so maybe admin can to add this recommendation to a general forum page if considered appropriate.
Their no is 01268 285535 and no I'm not connected with them!!