I just googled
natalie "the critic" designer jacket monk (probably not the most carefully honed search phrase anyway!) and this thread was the only relevant result so far, but I suggest you have a hunt online in maybe a few weeks when people have discussed the episode elsewhere, or maybe you could e-mail someone on the production team (wardrobe or whoever) if you're really keen to find it?
A quick search told me Ileane Meltzer did the wardrobe on the series in 2002, though I haven't seen anything past series 5, but if it is her (check the credits) google seems to show she has a Facebook page and a LinkedIn profile, maybe you could hook up and try asking? That may be a little OTT though!
I saw a woman with a handbag once passing me by on the underground here in London, and MAN I fell in LOVE with that bag, over a year passed and I kept wondering if I could make one myself, periodically tried to find one like it on e-Bay etc - then completely unexpectedly, I walked into a shop just to browse, and they had an identical bag right there for like £5!
Only mentioning that because I know what it's like to see something and fall in love with it, and also to say, keep your eyes open, and maybe the Fates will hook you up!