Thanks for the help everyone - I ended up getting a second-hand Hamster Heaven on eBay with the original shelf, and it's now just beside me (arrived this afternoon), freshly disinfected and deep-cleaned.
Now I'm just waiting on a PetPlanet order and I'm hamster-ready!
For anyone else who might have been interested, Bruno's did have them - £14.99 for the shelf (their current stock is blue), £2.99 for a green ramp, and £7.50 postage (I did ask if they did cheaper postage, they don't).
Thanks very much for the offer
gemleigh, it was appreciated.