I left Motability for a year in 2017-18 and used the “Good Driver” 5 year NCD with LV insurers.
To get over what Glos Guy said about comparison sites, I use one, can’t remember what one but doesn’t matter, but use a comparison site, find the best deal for you stating you have 5 years NCD then once your happy with a price keep the link to the chosen insurers open while you give them a quick ring to ask if they will accept the “Good Driver” letter and if they do, press the buy now button and that’s it.
That’s how it worked for me and I don’t recall them ever coming back to me for a copy of the letter so assume its all in the insurers data bases.