I have a few spare of my own design, with the DS1744W on a plugin module. Gets you a serial port also, Bluetooth, WiFi and USB serial. But no more VGA, no GPIB, and on these also no Ethernet yet. The latter still work in progress.
See elsewhere on forum what patchwork is needed on the TDS3000 main board. Not as hard as swapping the DIP 24 DS1742W module. That one just stays where it is.
Not in the UK. But in the united states of Europe. But if you hurry up, you can have me ship it to you before no-deal brexit is a fact...