Anyone have any ideas where I might find a fuel tank sending unit (3 line) for a 75? Any help would be greatly appreciated!

wrecking yard-possibly napa-most napa stores can get gas tanks, some sending units-good luck

Good luck, I've been looking as well.

I haven't call or emailed these folks but you might give them a try - http://www.tanks-to-pans.com/site/823208/page/502598

or this site
http://www.carestoration.com/gastanks.htm

or this company, I've bought from them, fast shipping and good product.
http://discountgastanks.com/?session=2917ab7d94db8a113670f6c8081218b9

Here is one for a Malibu, should work

http://www.ecparts.net/mgastank.htm

Three tube just like what your looking for and in the same year range.

That was about the only one I found.