Here in Canada the Bionx dealers are regular bike shops that sell top end bikes. The dealers see an advantage to being able to equip most bikes they sell with this system. I would approach a bike shop and give them the Bionx website and see if they are interested. If you order directly from Bionx they want it to be delivered to a bike shop for set up.
The high end bike shops like this system because it retains the handling characteristics of the bikes it is installed on.
Once a 350 W system is installed the only way of knowing it is not 250 watt system ( by looking at it) is the small 36V sticker on the battery. The motor has no markings and the throttle is available as an option on the 250.
I am not suggesting that anyone would buy this illegal system in the UK .......Just as no one would remove the speed restriction on their ebike....
You can buy just the motor from a dealer but you would be missing the great console that allows so much adjustment by entering codes for...Max speed assist or throttle, wheel size (rpm) ,speed motor will start, battery diagnostics etc. ( I have collected a few codes not listed in the manual!)
The battery is expensive but seems very long lived in my case of almost 2 years. (Flecc, I just checked a site and the price has increased to $1045 CAD ! I thought it would be going down.)
OHM are using the motor and console on their new bikes but have elected to use a battery by MOLICELL. It will be interesting to see how this bike fairs when tested by extra energy in the spring.