Sean I don't know much about Gateways, but generally parts like that are not easy to interchange from other brands. Not saying it's impossible though.
How old is the laptop? If it's old, there will come a time when it's cheaper to source an identical one via eBay than it is to buy the parts from the manufacturer. Then simply exchange the hard drive from your current laptop into the secondhand laptop (must be identical though) and off you go. If yours is only a couple of years old though, cheapest option is usually buying the parts.
I've done a few repairs like this on other laptops, and often it's a tricky repair, with multiple cables, wires, some delicate foil/shielding etc. Not the kind of thing someone without experience wants to try. If you haven't spent much time inside laptops, would be safer to take it to an expert.