Can anyone tell me of a Company that would spray paint interior plastic parts Piano Black, as required?

Somewhere in Berkshire or Surrey would be useful, or is this a fairly simple DIY job, and any suggestions as to what to use and how.

Take a look at this...

This seems to be the way to go, they can do most things, metal alloy plastic etc.

I have been looking into this, it looks a good coating, and as long as the lacquer is well done the bits will look good.

Its a myth

Theres no such thing as piano black.

Just get regular black spray can matte or satin finish and the best can of lacquer you can get hold of - most pro paint suppliers to the car trade can make you up a can for a few quid. Other useful items are a scotch cloth/block, tack rags, a can of air like you blow camera lenses with (or an air line if you have a small compressor), latex gloves and a face mask if doing in your garage just for the H&S gays.

The trick is decent prep, taking your time and ensuring you do it in a clean environment.

Use latex gloves to avoid finger grease when handling
Make sure your trim is in good nick, washed in weak soapy water and fully dry
Key it gently with a scotch cloth or block.
Blow this clean and then use a tac rag to make sure there are no lumpy bits to show up in the paint.
Apply several coats of the black basecoat - little and often is the trick, as is blowing the can nozzle clean regularly to avoid snotty blobs from coming out and ruining the finish, usually achieved by holding upside down and squirting couple of times. The idea is to get a solid even covering of black paint with as smooth a finish as possible. Don't get impatient and blast a great thick layer over as this will probably end up in runs and uneven surfaces that will show up a lot once lacquered. A gently spray from a foot away and a half hour between coats should do it - you can do some hoovering for the wife while waiting to earn brownie points !!
Once you have your matte or satin finished hockey sticks and other assorted trim you can let it all thoroughly dry for a couple of hours somewhere nice and warm, by a window indoors is good on a sunny day. If possible let it wait a day as this helps reduce reactions and lifting when applying the lacquer although we've sprayed cars in a single sitting when required.
Once you are happy its all cured nicely then you can tack rag it again and get on to the topcoat
This should be done as confidently as you can muster, maybe practice on a spray can lid or something else destroyable. The idea is to get a good solid coat without going too mad and ending up with runs. You cant do the little and often technique as that will end up with dull dry crap thats not shiney but with decent product, a bit of practice and some patience, a good finish can be achieved.
Use the same drying routine but with longer intervals of an hour or two between these thicker coats
A couple of coats should have you now looking at some very deep and very shiney parts - the more coats the deeper the shine usually up to maybe four coats max, and if you can get some decent car stuff from a paint shop then it should be lurverly !!
Last job for the extra deep look is a gentle flat and polish, but this should only be done a day or two after its fully hard. If you do this then get 2000 grit wet n dry paper and flat the last coat to get rid of the orange peel effect you are probably looking at (check against a bright light looking from an angle). GENTLY with a flat block rub the surface, you will now see dull lacquer with shiney pits in, this is what you have to work gently down to in order to get it all flat and even - this is what costs lots of money on showcar paint jobs as you have to do this between coats on the best stuff and suddenly you have spent an extra 10 days on the job and its suddenly a 10k paintjob !! lol
Once you have it all flat then you can use some cutting compound and rub that with a soft cloth to make the dull finish slightly less dull and upon close inspection you should no longer to be able to see the rubbing lines from the wet n dry, then finally you can use to finishing compound (and a mop bonnet if confident) to get it shiney again, but this is really pretty labour intensive and is easy to mess up but will end up with a really top finish that would cost too much to justify with a shop.
Then just apply polish and rest happily at night knowing you did something truly world class to your trim.
Then buy some new fingertips !! lol

I'm pretty sure I havent missed anything, but it is late and its been a while since I owned my bodyshop so I would like to just say I dont wish to be held responsible if you follow this advice, but its how i did anything - even my B&W's for my home cinema.

Good luck. Eat. Sleep. Race. Repeat.