A long time ago on the inter-web I saw bag racks that can be mounted on a bike without mounting braze-ons; trouble is, I have no idea where I saw it. Does anyone know of any company selling panniers or racks that can be mounted to a track bike frame?? Thanks!!
Just get those little rubber-coated steel bands that go around your chainstays, a lot of racks come with them for mounting the top part of the rack to the chainstays but you can use them for top and bottom, and on the fork as well. I am currently using them to hold a full fender to my frame, and would trust them with a rack with plenty of weight. My LBS gave me a few of these for free, they generally throw plenty of them out because they come with every single rack and they don't often use them.
Why not use an old road frame? It is criminally insane to mount panniers to a track bike! Heads are spinning! Countless corpses are rolling in their graves! The end times are near! Repent while you still can!
The mounting hardware folks are talking about are generally called P-clamps, and the rubber-coated stainless steel ones can be found at most good hardware stores pretty cheap if your LBS can't find them. They come in several diameters, so make sure you get one sized appropriately to your seat stays.
But I echo the above with my BWAHHH!! Who would even consider putting 50 lbs on a track frame? I'm certainly not one for the uber-specialization of bikes (I love flying by the fully-suspended folks while offroading on my road bikes) but a true track bike is already incredibly specialized for a very non-touring use. The bottom bracket is too high for stability, the angles are too steep for comfort, the tubes are too weak for heavy loads, clearance is too tight for comfy tires or broken spokes, etc, etc, etc.
Also, another issue with panniers on track bikes: pedal strike. With a tighter geometry, you have a pretty good chance of hitting the bags with your heels, which would make a ride quite uncomfortable and unsafe.