A good number of those types are near extinct now besides preservation, mainly due to the DDA laws. As I’ll mention quite a few times, bustimes.org will be of great help (and can be used for everything I’ve mentioned apart from Red Rose) when tracking down rarer buses like these!
Nimbus Darts can still be found on Jersey and Guernsey (the latter only a few). The Jersey examples seem to be mainly for school services though can be tracked on bustimes.org and do see normal service. What may be the only step entrance Dart / Pointer Mk1 you’ll find in service is the converted open top example used for Jersey sightseeing tours - see
https://flic.kr/p/2eFUAZ4). There’s some Nimbus Darts still in use with First Glasgow, someone more local can hopefully fill me in what services they can be found on.
Your best bet for Myllennium Darts is the examples with Southdown Buses, who use four of the LK55 registered ‘Project Pegasus’ examples on their services around Surrey, particularly the 409 and 410 routes are regular haunts (something on my to do list!). There’s also some similar examples with Lloyds Coaches, again maybe someone can fill me in on what these do.
For East Lancs Spryte Darts there’s one with Little Gem/Go Goodwins which sees use on tendered routes in Greater Manchester, particularly the 260/1/2 around Sale looking on bustimes.org (see
https://bustimes.org/vehicles/275209). There’s also two with Red Rose Travel around Aylesbury (Y358/359LCK). I think anything goes in terms of allocations with the Aylesbury Red independents, but if you download the Mytrip app, you can see them tracking on a map with vehicle reg plates (Red Rose aren’t currently on bustimes.org).
For MCV Evolution bodied Darts, again you’d be worth a trip to Aylesbury, as Redline and Red Rose Travel both have a few there. Recently Hulleys of Baslow have acquired some London examples from Metroline, they seem to be appearing on most routes, and being the Peak District I’m sure would prove an enjoyable day out. The other ones that may be of interest are two at Hedingham in Colchester, which are strangely 6-cylinder engined examples (I don’t know of any other such MCV Darts?).
Super Pointer Darts have been thinned out recently with the last Cardiff Bus and (former) Arriva examples retiring a few months ago. There’s two WJ52 registered examples left in use with Plymouth Citybus, though I understand they are sadly due withdrawal by the end of this month, due to impending service cuts. The third of the Aylesbury Red companies being Red Eagle can now get a mention for SN53AVK, a one time Lothian example which they normally use on the 61 service between Aylesbury and Dunstable. Select Bus Services have SK52OJG, another former Lothian one, which you’ll normally find on Stafford locals, or the 877/8 to Wolverhampton. Occasionally Moving People use Y177CFS, yet again ex Lothian, on their 33 service in Blackburn. There‘s probably more of these to find if you know where to look.
I can’t think of any Wright bodied Darts still in use, another DDA casualty, but you may be interested in a pair of former First Devon (latterly at Somerset) WK02 plate Volvo B6BLE/Wright Crusaders that occasionally see use with Ashcroft Travel around Runcorn.
The easiest way to sample a Plaxton Primo would likely be KX08HMA with Whippet on the St Neots Town services, which it sporadically operates. There’s a few others listed on bustimes with Holmeswood Coaches, Ulsterbus and West Coast Motors, but none of these seem to have been used recently.
Hopefully this helps you with planning a few trips on these buses!