I have seen lug bolt covers somewhere on the internet. I just don't know were.
Everyone that I have seen require/comes with a special tool to be able to remove them to get to the lug bolts. Something to think about.
What happens if you loose the special tool?
It might be more cost effective to just get new bolts (chrome?), or pull the old ones out, clean them up and possibly paint them.
edit: just did a Google search (lug bolt covers), and you will find them.
Several years ago I tried the covers - they looked cheap so dithched them (a friend with a Range Rover took them.....!). There are several firms that do chrome bolts or just get a new set from BMW or one of the several suppliers on the internet. The old ones will clean and just a regular freshen up with something like WD40 will keep them looking reasonable.