Again take a look at the RS. They have tons of grommet references. Quite sure they have what you are looking for
I have an RS Account. They used to have a reasonable range, but I've found in more recent years, they have gone largely to the cheap PVC based Grommets. Also, they all have a fairly large hole through them for the cables, while for some jobs, this is fine, but for many in the Mini, this is undesirable. The Hole sizes through the bodywork are just about all worked out around the Plug Sizes that are fitted all over the wiring looms, the biggest being those that need to pass through the firewall in to the dash area, however the size of the loom following these plugs is very much smaller. Using a common Industrial Grommet for these situations isn't a good idea (and could be questionable in terms of Roadworthy) as they will let fumes etc in to the cabin area.
I have at times, used Blanking Grommets and punch appropriate sized holes in them for the job at hand, however, with the PVC Based Grommets, there's no stretch or give in them what so ever, so the larger parts of the loom (plugs etc) can't be passed through them.
Another possible issue with buying from RS is that they tend to ONLY supply in bulk lots of 50 or 100, I've not found them offer a single grommet.
https://uk.rs-online...rchTerm=grommet
From their range, this appears about the closest to what unburnt is after;-
https://uk.rs-online...ions=4292006544
