Before you replate you will need to remove the exisisting plate,this the company will do for you.In the S.East try Kent Metal Finishers in Gillingham 01634 377592. You get what you pay for, the better the copper undercoat is the better the top coat will last. The price used to be worked out on the weight of the artical to be chromed.
Some time ago I got a quote from a company called "Winchbrite" , 35 Greenvale Rd., London SE19 1PB.
Tel. was then 0181 850 5631 from which you will see that it was a few years ago - I don't know if they are still in business. In the end I didn't get it done so I can't comment on the quality of the job but the quote was reasonable.