Mk5 sliding door

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Hi,
I have a 1999 smiley that was an ambulance all its life, it's done 13k miles in all that time so can't have been many emergencies near it. I'm converting it to a camper but need a bit of help with an issue with the nearside sliding door. It had been closed up when it was fitted out as an ambulance, I've managed to open it up again but the top roller and rail are missing. As I'm based in Ireland, there's not as many of these old ladies around to find second hand parts. Could anyone point me in the right direction as to where I might get the parts in the UK. Thanks