Titanium Seatpost for Brompton Bike Superlight Diameter 31.8mm Folding Bicycle Seat Post - AliExpress
Amazon.com : Titanium Gooseneck Seat Post for Brompton Bicycle Saddle 31.8mm Folding Bike New Type Rod 550/580mm Gr9 Ti Accessories (550, Gold Color) : Sports & Outdoors
AGEKUSL Seat Post Seatpost Ti Titanium For Brompton Bike 31.8mm 550/580mm | eBay
Conversion of A-Line to H3R with titanium stem and seat post - full parts list in comments : r/Brompton
Jtek Titanium Seat Post for Brompton - Jtek Engineering
Brompfication Titanium Seatpost Brompton titanium seat pillar – TITANIUM BIKE