Essentially all OEM trim items have been obsolete for years & stocks run down with the aftermarket filling the gaps in some cases, but generally it's of poor quality.
As for service items I decided to treat mine to new ign. components last year, plug & leads were no problem but the distributor cap & rotor arm were such rubbish that I cleaned up my original 'made in England' Lucas items & returned the new stuff for a full refund .. the supplier didn't argue, I guess that's all they can source these days.
Thankfully mechanical components & rotating electrics for the Classic are still generally available, but again the quality is variable & basically you get what you pay for.
The good news, considering how much of a rot-box the Classic can be, is that body repair panels/sections are generally available.