Current (07-07-2023) Places to buy Gateway interface pictured here and radio:

Gateway Interface Box:
https://www.ebay.co.uk/itm/404076750827

CRT Space-U Radio:
https://www.pjbox.co.uk/products/crt-space-u-vhf-mobile-radio

Don’t forget you will need a PMR 446 antenna and 13.8v power supply for the CRT

You will also need programming cable and software to setup!

With the Interface box a USB a to B lead, 2 x 3.5mm audio cables and a PS2 / 6 Pin Mini Din
Cable to connect to the radio will also be needed.

The pictures in this section show all needed connections to link this all together with a CRT 
Space-U and setup a gateway!

The USB driver for the interface is also in this downloads section to make it work with FRN.