You need to check the whole set up; there are so many variations in relations to ; the brakes; can be Magura hydraulic rim brakes or drum brakes or others; wheel sizes; front wheel sizes can be 17 or 18 inch...check the tyre sizes; if you have got a size that can take a Kojack tyre thats a good thing; if they take the Hutchinson's they arent so good ; once you have checked the size then
https://www.sjscycles.co.uk/ are good for most tyres. Then the back wheel; generally 24 inch, itself an unusual size; tyres available; the thin tubes can be a bit tricky but SJS again. If you need a chat about spare parts DTEK [ Kevin] [
https://www.littlethetford.net/?page_id=529] is worth a phone call and can supply nylon idler wheels and handlebars which he has made. If based in London Bikefix can help with possible servicing. Theres any number of set ups of the front derailleur; i have a triple chain ring set up; and 7 speed rear derailleur. They have different handlebar gear changers, twist grip or trigger shift. Once you have had good look and assessed what you have you can start to make improvements. The best thing I ever did was get smaller nominal 17 inch 32-369 17 x 1 1/4 from a Moulton set up... as the Kojack tyres are good and available. The seat set up can have problems; its a tension based strap... which can dissadjust itself; I have solved this by using a seat cushion from another recumbent like this
https://www.ventisit.nl/en/applications/recumbents/. You can see you are not just buying a bike but an entry into a whole new world. Its quite a well supported and they are raced regularly at these meetings;
https://wc2024.bhpc.org.uk/ and
http://forum.bhpc.org.uk/forums.html ; welcome to the Kingcycle world .