I still want to find a #4 in .22LR, but this really scratched an itch I have had for awhile!
Chooks9,
Simpsons Ltd has at least 4 No4 22 Training rifles and an original 22 conversion kit on their website.
I don't work for them, just peruse their site and have always been treated well, though some of their prices on consignments are prayers.