It's basically Honda OEM for 95% of the Insight specific stuff, the other 5% like oil filters/brake pads etc can be sourced via equivalents or pattern parts. Personally I use all Honda parts.
Stuff like windscreens/glass etc can be a royal pita as that's Honda only, sometimes out of stock and comes from Japan or the European warehouse. I'm tempted to buy a windscreen and keep it in stock like I do some of the other bits.
IMHO as a group of UK enthusiasts we need to keep an eye out for every car in the UK, stop and talk to the owners, put notes on them, find out who owns them all, keep a database and group buy every crashed car to strip them down and store parts away for future use. Perhaps we should design a note/business card giving details of this group/forum, keep them in our cars and put one on every one we see in the wild.
I've got enough parts now for my own cars for most of the exotic bits but it is a worry in the future. Things like Cats and the rear suspension member are very expensive.
I predict several serviceable UK cars will go to the scrapyards in next few years as the requirement for a new IMA battery at £2000 will make them uneconomic in their current owners eyes to repair