Is there a place online where I can find out whether a particular G3xxx callsign has *ever* been allocated, or is that something I could only dredge up from old paper call books?
From time to time Ofcom release a spreadsheet of "available callsigns", but these are, obviously, out-of-date pretty much the moment they're released, and they don't seem to make a habit of releasing them regularly or frequently. I think the latest one I saw was the result of a FOI (Freedom of Information) request, dated early in 2019, and that's the most hideous jumble in no obvious order, with all sorts of random entries that make little or no sense. Even the "Allocation Date" field seems a bit random.
In this case however, I did pass my UK RAE in 1971 and would be thrilled to obtain a call of the right "vintage". If that could be one that has never been allocated, it would take care of any possible objections I think.
1971 seems to coincide (as far as I can figure out from that spreadsheet's somewhat inconsistent "allocation date" column) with the last of the G3 and the first of the G4 calls.
I can't find G3WSY in that spreadsheet, so you might be able to get it. G1WSY and G4WSY are marked as "Reserved" with no date. G6WSY was allocated 1983, G8WSY in 1984 and G0WSY in 1995.
G3EDM is marked as "Reserved" with 3rd June 1948 as the date. G4EDM was allocated in 1975, G6EDM in 1981, G1EDM in 1984, G0EDM in 1986, and (unusually) G7EDM in 1989. (G2, G5, G7 and G9 calls aren't usually issued.)