Kingdom Arc Garden Swing Seat - very cool, but could DIY with PVC? Maybe not the support frame.
I like the idea of a swing on a frame under a tree instead of attached to the tree. With Oliva engraved
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Wooden Swing Seat - Large Heavy Duty 3 Seater Outdoor Garden Swing Bench | eBay £400
Quality wooden swing seat and Pergola
Romantic suburban garden - Traditional - Landscape - east midlands - by Jane Harries Garden Designs
Garden Swing Chair - You can get swings like this from granit. We'd need sturdy trees or a custom built stand.
Swing Seat - Wooden Garden Swing Seat With Wood Frame - 2 Seater Swing Bench | eBay £350
DIY Swing redo (links to commerce page) - just grabbing the idea.