Is G.Fast still being sold?
Yes, via Pulse8 (no contract for G.fast 330/50 @£57.00 a month) Must use your own G.fast router with one off activation fee £79.50
via UnchainedISP (12 months contract for G.fast 330/50 @£56.99 a month) Free openreach G.fast modem (think it no longer now by Openreach) and free activation fee
via BT Fibre 250 (G.fast) 330/50 (12 months contract @ £55.99 a month) with BT Hub 2 (£29.99 P&P with activation fee)