The covers for the older style Riot Kayaks seat are the following:

Seat back:  https://boutiqueborealdesign.com/products/touring-backrest-for-sea-kayaks

Seat base cover:  https://boutiqueborealdesign.com/products/seat-base-touring-black-1

You will also need the following:

1 set of Cam Buckle : https://boutiqueborealdesign.com/products/cam-buckle-25mm-wide-with-webbing-attachment-2pcs

2 x Phillips Pan Head:  https://boutiqueborealdesign.com/products/screw-phillips-pan-head-stainless-steel-wlm5-x-16mm

2 x Washer: https://boutiqueborealdesign.com/products/washer-stainless-steel5-16-1-2mm

2 x Nylon Lock: https://boutiqueborealdesign.com/products/nylon-lock-m5-include-capnut-m5-qnty

1 x Pinetree Fastener Kit  https://boutiqueborealdesign.com/products/pinetree-fastener-kit-includes-10-pinetrees

(need to drill two holes in seat base to install the Pinetree Fasterners)