Hi,
Welcome to the QB. The D9 started production around 1895 until lasted until late 1905 when Singer gained control of Wheeler and Wilson. Singer kept the model going for a few more years until replaced with the 9W7.
Needles are commonly sold as 127x1 or Boye 18. The needle is about 1-3/4" long with a 1.75mm shank with flat on one side. You might need to buy a used faceplate to get the spring. The bobbin is often referred to as a donut bobbin. Make sure it has the hole in the side of the bobbin for the thread end as there is a similar bobbin without the hole for an earlier #9. With patience these can be found online.
I've always considered Wheeler and Wilson the Cadillacs of antique sewing machines. Good Luck.
Jon