Thanks for all your help guys - kootenaigirl's advice was right on. I bought a faucet from Canadian Tire (their part number 062-1029-0) for $32.99 plus tax, and it works perfectly slightly different from the one kootenaigirl recommended). I actually wanted to replace the standard hand pump, which takes water from the onboard tank, with a faucet tap that I could connect to my electric water pump, which in my Trillium only serves the toilet. I had to make an adapter plate both to cover the hole left by the old hand pump, and also because it is effectively impossible to attach the new faucet otherwise. I did this with a piece of plastic cut from an old house dryer vent. Photo attached.
One happy Royston