Hi Jon
Ash had a dreadfull time getting a decent feel to the brake pedal.
After hour's & hour's of bleeding the system, his new master cylinder tuned out to be the culprit
I would persist in bleeding the system for a while longer, if no joy, look for a likely cause elswhere
Golden rule of mechanics, even a new component can prove to be faulty
I hope you get it sorted
EDIT
Just to add
The symptoms you decribe are typical of trapped air in the system.
Have you been bleeding the system in a logical sequence ?
Rear brakes first, Furthest one from MC & then the next one.
Front's next, again furthest wheel from the MC first.
Then repeat if needed.
Sometimes it will help if you push the pedal down sharply & pause at the bottom for a couple of seconds to allow the MC time to refill.
Pressing the pedal sharply has been know to shift stubborn air pockets.