Hmm, it sounds like this is something that you should just do for yourself. This kind of work isn't easy to arrange when you're not actually there. Presumably, you know what your composition should look like and that's going to be extremely difficult to communicate to somebody not in the room.
There's also the issue of lighting, even with the proper composition, there's a ton of ways one can light the still life which will look very different.
If you use pre-existing stock, make sure you know what rights you're buying. And just buy the rights you need. If you don't need to use the photo itself, try to just buy the rights to make a derivative copy. Distribution can also be an issue, if you post it to the web, you'll likely need worldwide rights or rights to post to the web.
As a result, it's probably a lot better to just learn how to do it yourself, as it's not easy at all to arrange. And once you learn to do it yourself, you have so much more control over the materials you generate.
Plus, it's just a camera, they only bite when you stick your finger past the mirror. :-P
The process for finding photographers usually means just searching the web for us and when you find a portfolio of work that you really like you contact them about pricing. I would warn you though, while what you are looking for sounds pretty simple it can actually be a fairly expensive process since it involves hiring a model and actually setting up a shoot. I think your best bet is probably just to use the microstock photo agencies like shutterstock or istock and just find your reference photos from their existing database.
It's very likely for the models I will not hire anyone, but for the still life I'd really like a photographer to set up what I'd like to draw. The model work is very basic posing so generic stock would likely be fine.
Thanks for your help though, I've only really hired models/photographers as a graphic designer and never for drawing resources so I felt like a total fool and wanted to try and word this as short and simple as I could!