Soulpad and BelltentUK have a monopoly with a company called Obelink in The Netherlands. Obelink send any product to the UK except the bell tents, which they only ship to Soulpad and BelltentUK who mark them up significantly to sell as boutique glamping tents.
I got lucky with mine, got someone on the phone at Obelink who obviously hadn't been informed of the embargo and posted me one for nearly £200 less than the identical Soulpad. I got the unzippable groundsheet version so I could unzip and roll the sides up. I never have, but it's a nice option on a hot day.
Have a look on Aliexpress, there are loads of them much cheaper than anywhere. I reckon quality varies, my Obelink is rated 'heavy canvas', but a bit of looking around should find you something.
Eric Methven had contact with a lady in England who imported the best canvas from India….by the tonne….and she was making tarps, belltents and the like. It still worked out cheaper than buying the soulpad things.
It is car camping the OP wants it for right? Easy up and down for an airbeam style tent. They've been arround for a good few years now and are into their nth iteration. That means a lot of problems are designed out of them. Each beam is often separated. In some it'll actually stay up even with one beam deflated apparently. Plus price has come down a lot since they hit the market.
BTW some brands have tested and marketed their airbeam style of tents to rather high wind speeds. Not as high as their top range of poled tents but then not many family tent brands would rate their tents so high. I'm thinking of Outwell here. Their poled tents in one or two of their ranges have seriously high wind ratings. As high as geodesic mountain tents i think. Their air tents also have decent wind ratings i believe.
My personal view of these bell tents and other canvas tents are the fabric needs more care. We had a frame tent when i was growing up. It was a real problem if it got wet before packing up. Plus it was such a high bulk item. The fabric part of the tent filled the middle of the rear bench seat of our car. Me and my sister only just fitted either side. It was a great thing to put between us on long tiring journeys. Stopped squabbling when young and became a table when older for cards and things. I would not want to carry such a tent these days.
We got a 6 man Vango tent. Cheap and it stood up to serious winds although a couple of poles twisted against each other at the top so we couldn't get them undone. We only replaced it with a 4 man plus enclosed porch extension due to tree pack size. It half filled the car. The 4 man plus porch was half the volume. That's worth factoring in.