Having been through this myself in an attempt to use a reflector all by myself:

1. Something like this - its an adjustable arm that attaches to a lightstand and lets you pivot the reflector around. It works fairly well with two/three big downsides. One, the stand really really needs to be weighted then, it just too off balance otherwise. Two, it takes up A LOT of room when assembled, don't plan on using the whole lightstand+reflector in a small area. Three, its just not good outside - its a giant sail. You can really only use it inside.

2. For using a reflector solo I've had more luck using one of these - a triangular reflector with a hand grip on it. You can hold it with one hand and click the shutter with the other. Its difficult to do just right though and really works best for head shots. The advantage is that you can get one of these and clamp it really easily by the handle though. It's also small enough to put on your hip and carry it around without banging into everything.

In general, its really, REALLY hard to use a reflector by yourself. It seems like when people mention how good a reflector is, they just glaze over the fact that a second person is really needed. Even with the above methods, its often easier just to break out a flash if somebody isn't around to help you - that way I'm not trying to balance a reflector in one hand or keep something from blowing over (even with sandbags).