They contracted Stronglight of France to make the cranksets ,
they use a Plastic snap on chainguard , that fits directly on the chainring.
there is only 1 per size , the minus is 44t.
http://www.sjscycles.co.uk/brompton-...44t-prod31223/
the plus is 54t,
http://www.sjscycles.co.uk/brompton-...54t-prod31229/
the standard 50t.
http://www.sjscycles.co.uk/brompton-...50t-prod31224/
Your dealer you bought from should be able to order and supply the replacement part ..
Or SJS will ship out of UK.
Also, I *believe* am missing two plastic caps.
One that covers the crank arm bolt,
any generic crank arm dust cap will do
and another that covers the non-folding pedal bolt.
there was never any. it's just a generic 9/16" right hand thread , pedal.
you can fit another pedal if you wish.