You can get the parts at any good electronics supply place. But, beware that because there is a difference in the spacing on the 44pin you'll have to do some hand wiring to get everything lined up correctly.
It's much easier to just buy an adapter or cable premade (same place that sells the parts will have them).
Examples (forget eBay, you don't need an "Amiga" cable)
44pin to 40pin 9" cable
http://www.cablesonline.net/940pinto44pi.html44pin to 40pin molded adapter
http://www.cablesonline.net/44pinto40pin.html
