Jerman is right about E39.. You need a heat gun to melt the glue that is holding the glass cover from the casing. The high beam is made from metal and can be done easily but the low beam casing is made from plastic. Chances is that you will melt the plastic casing.
For e36 and e46, the front cover (glass for e36 and plastic for e46) can be easily replaced by removing some clips.
Jerman is right about E39.. You need a heat gun to melt the glue that is holding the glass cover from the casing. The high beam is made from metal and can be done easily but the low beam casing is made from plastic. Chances is that you will melt the plastic casing.
For e36 and e46, the front cover (glass for e36 and plastic for e46) can be easily replaced by removing some clips.
what I am saying even if you can buy the cover alone, it is difficult to change it. hence, no point to source for new cover except to get the whole unit.
guys i have bring my car to polish, than they also polish my head lights, using maguire product, it works, but the guy need to polish few times as my car is year 97, now looks new again
Actually you can even clear up the plastic covers with the normal polish and wax used for the paintwork. Try it first before sending it to a professional car wax shop.