There have been ex-MOD radiosondes for sale on Ebay UK for a while now and
there seems to have been no shortage of buyers (and least one person who
seems to bid on them all). Some of them include a GPS receiver, though not a
fully featured one - it reports only how much it's moved rather than where
it is. The GPS versions fetch a higher price than the ones without so
presumably there's something you can actually use these modules for. Does
anyone know what?

Perhaps I should buy one rather than risk being the only Radio Amateur in my
street without my own radiosonde....

73
Hugh