You could try phoning the people who sell the Sky rat. I think they probably just import it from Germany. It used to be for sale on German Amazon but the seller is not shipping to the Uk any more. I think the seller in the Uk is ok if you read their blurb on their webpage but have never used them myself.
The 120cm Speedy Gonzales is a Skyline cage though (the ones that make the Barney and Alexander). And it's the only one I know of that is bigger than a 100cm cage and has narrow bar spacing. It is pretty huge! Cypher sent for one once and then exchanged it for the 100cm one.
There are other 120cm options (or 115cm) which are tank style rather than cages. There's the large Eco Habitat (wood and perspex), which Zooplus sell. That has a very good floor area as it almost 80cm deep and is 118.5cm wide
. Internal measurements are 115cm by 75cm. I think that's about the biggest floor area you can get for a Hamster cage, without doing a diy cage, and it's easier to set up than the speedy gonzales cage which has fall risk issues to sort out.
With the Eco Habitat you can put masses of substrate in so a hammy can dig tunnels. It would need a freestanding platform or two with deep substrate - one for a wheel to stand on, but it would be a great large cage for a Hammy. Costs £149 on Zooplus. People who have had them tend to paint the wood parts with plastikote - but it's only the thin bits of wood at the edges really. The base needs protecting too - I think one person put correx sheets on the base (plasticised corrugated cardboard) - some kind of waterproof covering on the base inside would be a good idea, although with very deep substrate it's unlikely to get wet at the bottom.
The lid has 2cm spacing though and hammies can escape through that, so the lid needs meshing on the outside ideally, but it would just be a cage of a piece of mesh and a stapler. Or just make a new lid out of wood and mesh, which would be lighter.
I also saw Teddy's set ups in the Critter nation - and they are great. But in the US there are very few cages to be had. I think it's difficult to adapt to give enough substrate depth - the trays are quite shallow and if it's any higher than the trays it will fall out when the doors are opened. You could make a perspex sheet to go inside the trays to make them deeper but that would add to the cost. I think they are lovely big cages but hard to adapt for a good depth of substrate and very pricy.
If you don't have space for anything with bigger floorspace than 100cm, then something like the Skyrat (called the Carlos cage in Germany) is good. It's a bit like two Barney cages on top of each other. There is another seller in Germany - I'll see if I can find it.
I think I would go with the large Eco Habitat, or the Speedy Gonzales 120cm or the skyrat/carlos.
A German seller sells this one on ebay and posts to the Uk. It's like the Skyrat but has 6mm bar spacing! I wanted to get this a year or so ago but it wasn't available for Uk postage then.
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I'm not sure which German seller Cypher used for her Borneo cage (same as the Speedy Gonzales but without shelves) but they were very good at exchanges and returns or things arriving damaged.