Presumably one of the two Maintenance Units at RAF Sealand - 30 and 47.
Here's what they have at Kew -
http://discovery.nationalarchives.go...e+unit+sealand
I wouldn't be all that hopeful that there were much more than the odd references here to captured aircraft. I believe Phil Butler delved into this when researching 'War Prizes'.
If you get nowhere with getting anyone to look into this, you're welcome to send me a PM and I'll take a look later this year but I' not going up for a few months.