Bottom bracket replacement bearing I have been looking for a press-fit bottom bracket replacement bearing for a Giant Fastroad SLR1 (2016 model).

The markings on it identify it as an FSA 19mm diameter, that is the spindle is 19 mm I think.

I took it to my LBS, they did a botch job with some replacement bearings, not the full unit, which I had to re-adjust myself as they tightened it far too tight.

Can anyone recommend where I could get some replacements from please?
Your bike has an FSA Omega crank that does in fact have a 19mm spindle. All press fit BB types either use a 24 or 30mm spindle, so you must have a special BB unit. I'm guessing that it's an FSA 19mm to BB86.

You should confirm that you have a BB86 frame, you can do that by measuring the width of the BB shell, it should be about 86mm.