Welcome to CCUK, but ebay is your best bet for finding tartup parts. Back in the mid to late 2000s, this forum might have had a vibrant "parts/upgrades for sale" section but it's a minimum 15y.o. car now and most people just want to keep it running them to work.
I'm weening myself of ebay, having tarted up my car nearly as much as I can, but I used to have a sad watching addiction and I have learnt that (even as of now) the word "Irmscher" in the title still attracts mad bidding for bits of stuff considering the car it's going on struggles to reach £1k if sold off. I'll let you know if I see one but I think the last gear knob was >£30.
There was a banged up Combo van recently sold (maybe off-ebay with a lower accepted offer) for £700 that had Irm grille, chin spoiler, gear and h/brake, door pins, steering wheel and pedals. With a disc rear axle and 17" Irm alloys, it was probably worth breaking up or as a donor to someone with a project. Even the horrible Irm fuel cap (a sticker over the existing GM flap) sells for silly money.
Irmscher Fuel Cap Cover. Genuine Part New.
www.ebay.co.uk
You are looking at a irmy fuel cap cover removed from a corsa c. 5- Credit or Debit Card (Fees Apply). Condition: Used / Second Hand Car Part. This Item has been checked. Overseas & Highlands & Islands are extra.
www.ebay.co.uk
I'll flag up any items, but there are no bargains out there, sorry to say.