You can do this for about Â£30 and I personally use a company called Hodges and Co, Richmond Road, Catterick Garrison - 01748 832288. You might need to provide certain accoutrements like shoulder titles or buttons, yet again they may stock them. I have heard that in some instances he disposes of stuff that might no longer be Grade A standard so you could always try that approach.
If you are a SNCO you should already have the trousers as they are the same with the Mess dress. www.mess-dress.co.uk are quite pricey but they squared me away with a tunic for my wedding - it looked the nuts.
I have a tailor made set of Corps No1's worn only once, but on the premise that the wife isn't going to sell her wedding dress.....shame really we could have come to some arrangement.
On the subject-there is a story which, may or may not be true (but knowing the individual concerned it probably is)
Newly appointed Corps RSM is in office with young subby who has disgraced the uniform to such an extent that resignation is the only course possible. "What can you do for me RSM?" sobs the subby"Well, Sir we are about the same size so I'll buy your Service Dress off you!"