I had to remove a seat post reflector because of an underseat pack. I have a Sunlight rear bike rack and I'm having trouble finding a reflector the I can put on the rack. Any suggestions?

A combination of the PBSF and their rack mount adaptor might work. You could also buy e.g. the Serfas Stop Sign blinky, which AFAIK has a shape that will fit on a standard rack mount, and an integrated reflector.

Thanks. I think I'll order the Serfas Stop Sign Taillight.

Not familiar with that particular rack - what I did on my commuter: purchased a cheap trailer reflector at an auto parts store and zip tied it to rear of rack. Using a pair of hose clamps, I clamped a length of pvc pipe across the top of the rack; a Dinotte tail light is on one side and a backup PBSF is on the other. Keeps the lights above the panniers I use. Cost was maybe $2 for the reflector as I had scrap PVC, zip ties, and hose clamps.

It sounds like there are two types of rack mounts for lights. I suggest you read through these threads:
https://www.bikeforums.net/showthread...t-on-rear-rack
https://www.bikeforums.net/showthread...ed-tail-lights

The Cateye 1100 also fits on the US standard reflector mount (two vertically-spaced holes).

I have a titanium bike and a custom titanium rear rack. I think I would prefer a quality clamp made of titanium or at least aircraft aluminum. But that is on the order of what I need as well. Great idea. Simple. Effective.

After contacting the company that makes the Serfas light, I can't use that one. The company stated the rear rack would have to have a place for screws already in place. My rack has NO screw holes at all.

Mine is also missing holes, and I really want to keep it that way. So I'm thinking about getting a strip of aircraft aluminum from a shop at the airport and making my own clamp of some sort. I would much rather buy a factory made one off the shelf if someone could point me to it.