Hey all, I would like to consider replacing my master cylinder with one from another motorcycle.  I wish I could find one that is made by a major manufacturer (not imported eBay weird junk), doesn't have the big square fluid reservoir, and has aftermarket options for levers.

You know where I should look for something like that?

If your in AU i could sell u this one.PERFECT working,and great cosmetic condition;it's just that i recently bought a new Yamaha MT-09(US designation FZ09) and i no longer require it.Besides,the stock master cylinder for the GS works very well with the Hayabusa.
RE this thread and my review thread after.
http://gstwins.com/gsboard/index.php?topic=69375.0
http://gstwins.com/gsboard/index.php?topic=70422.0

There are tons of options for replacement brake levers for the GS. The issue is whether you want a matching clutch lever, due to the oh-so-unique clutch perch that Suzuki decided to use for the GS500. You can replace the clutch perch with one from an SV650, for example, and open up tons more options for matching aftermarket brake & clutch levers. Beware though, if you do the clutch perch swap, you may need to watch out for cable clearance against the gauge housing. It's very close unless you swap the 45 degree bend OEM clutch cable for a custom 90 degree bend cable.

My point is that if you only wanted aftermarket levers, you don't need to swap the front master cylinder. Now, if you don't like the "box" look, that's entirely different. 

Yah it is the box reservoir that I'm hoping to eliminate.  I would like the look of my bars much more without it

Lucas, look for the bore size of the piston in the master cylinder. It should be cast into the bottom of the housing, and will say something like 5/8". That's what is really important for swapping out an MC.

And don't worry if the donor MC is made for dual calipers - the master is moving whatever amount of fluid regardless of how many calipers are hooked up to it.