Small nitpick, but the ZX Spectrum 128k itself is not the base 48k model :)
When I said "stock" I really meant a basic 128K/+2/+3 machine and not one of the interesting Soviet/Eastern European clones with advanced capabilities that some portions of the demoscene adopted.
In the Iberian Peninsula, 128K models were all over the place.
Not really in UK or other European countries (besides the Amstrad almost-knockoff).
It is strange that on UK, Speccy birthplace they were apparently rare, given all the Crash and Your Sinclair magazines I owned at the time, and related content.
Amstrad bought Sinclair in spring 1986 and they ran down the remaining 128K+ stock, meanwhile the grey +2 was already ready to manufacture - they'd already designed the case and reversed engineered the 128K+ to get a head start. It was in the shops by that autumn.