Check Amazon and eBay using '18" ide ultra cable'. For eBay, sort it by lowest cost (including shipping). I like the 'StarTech.com' cable. (I wouldn't recommend this super bright yellow cable at Amazon as the middle connector wasn't connected on two of the cables that I bought.) When you see something, just look for the blue connector (for connecting to your IDE to SATA adapter) and that there are two other connectors (which will be used for connecting to the mobo and DVD drive).
(I also use the red StarTech.com IDE2SATA2 adapter.)
https://www.amazon.co.uk/s?k=18%22+ide+ultra+cable&ref=nb_sb_noss
https://www.ebay.co.uk/sch/i.html?_from=R40&_sacat=0&_nkw=18%22+ide+ultra+cable&_sop=15