Anyone know where to get a replacement greenhouse door

Hi pavery, it might be tricky as there's no standard size/fitting for sliding greenhouse doors.  Most of them have wheels embedded in the door frame which must fit the sliding rails exactly.  If you can identify the make/model of greenhouse then you may be able to get a spare door. This is a great place to look for greenhouse spare parts:

http://www.greenhousewarehouse.com/greenhouse-spares/

Alternatively, perhaps you could cut a piece of 10mm twinwall polycarbonate sheet to size and fit some normal hinges to make a door which opens outwardly, with a hasp and staple on the unhinged side to keep it shut?  I think that's what I'd do.

Doing that should be OK.  If the aluminium frame seems a bit on the thin side to support the weight of a door though, you could drill through it in several places and screw on an upright length of wood to provide more support, then screw the hinges to that.

You're welcome.  If you do use twinwall polycarb sheet, remember to seal the open ends with tape as soon as you have cut it to size, to stop spiders etc from crawling into the hollow sections.  Once they're in there, it's the devils own job to get them out!

It must be difficult as sliding greenhouse doors doesn't have standard size. Many doors have wheels fitted in the door frame. Just measure the size properly and get the best sliding door. 

Dont know about the doors but for the glazing a cheap and easy way to replace theys is with Polythene Film and polly tunnel tape.

You might be able to use washers and nuts and bolts to make up a set of "wheels" to fit the sliding door that could be a plastic glazed wooden frame.  Depends how handy you are.