I once made one many years ago- v thin batting making a quilt, with an additional layer to make a duvet cover type 'envelope'. I used it as just a quilt in the summer and with a duvet in the winter. They do work I've never seen such a thing for sale though, I would imagine it would have to be a special order thing from craftspeople.
You could have a go at making one? I once made a big patchwork with the plan of stitching it on to a duvet cover to simplify the process, only I still have the patchwork and have never got round to putting it on a duvet!
I have always put my patchwork quilts into the dryer and they've been fine. They're not very thick though, just a layer of batting between the fabric layers. More like bedspreads. I've never seen duvet thickness quilts. You would need to stitch through the duvet filling to achieve the quilted effect and this would be a challenge I would imagine.
It wouldnt withstand lots of washes. It would be better to have plain bedding and a patchwork bed spread. My mum makes patchwork if you want to pm me and I can pass on her details - you choose fabric etc. She does it properly though - it's all hand sewn - you get what you pay for IMO!
My mother bought them in the USA but I confess I know now where. I assumed you've asked Google.
Local artesans, craft fairs, craft shops who run workshops and have talented contacts. You can get it custom made in colours you liked, with patterns you prefer. I've been asked to make a double-bed-size patchwork bedspread for maybe £50-£70 but not actually sure I'd cover costs. It's a much bigger project than I have done before. And I'm only a beginner, really. Some of the ladies I did patchwork course with often sold their works.
Somewhere like LinkedIn might have folk on there who could make a quilt for you.