Ebikes Direct had some spares for Freego after the company folded, but they do not stock KT stuff. PSWPower is a company many here have used.
FreeGo Spare Parts - eBikes Direct
www.e-bikesdirect.co.uk
This controller will work with your bike along with a new LCD3 display.
36V/48V 350W Brushless DC Sine Wave Controller ebike Electric Bicycle Hub Motor Controller with right output
www.pswpower.com
KT- LCD3 kt lcd3 ebike 24V 36V 48V intelligent black Control Panel LCD Display Electric Bicycle bike Parts for KT controller
www.pswpower.com
You will be able to reuse your PAS sensor, throttle and brake cut outs, but you will need a speed sensor.
external speed sensor for controller of electric bike conversion parts speed testing sensor
www.pswpower.com
If you don't want to deal direct with Chinese company, then Torque Tech in the UK should have what you need and will help answer any questions you have before ordering, but will cost more.
The Layer Laboratory : A dynamic additive manufacturing enterprise. Providing practical solutions to real problems with unique & innovative products. UK stock. Free UK Delivery. Fast dispatch. Great service. Unbeatable support.
torquetech.co.uk