Funny, but when I shop at Walmart or Target, they not only have 16" tires (not the best, but good for an emergency), but they both carry 16" innertubes. These are Schrader valve, so I'm not quite sure they'll fit a Brompton. I believe a Brompton is Presta valve? When I finally do get my Brompton I'm drilling out the rims,... Schrader is so much easier to find in the USA.