Placerville may be a little out of the way for many models, but you may be able to find some in the Sacramento area, or even the SF Bay area, willing to travel. Or, as Jorge mentioned, try to find a photographer in a larger city who might be willing to rent his/her studio for a shoot there.
Another photo forum you might try is the Black & White Photography Forum (http://www.bwphotographyforum.com/). There are a couple of SF Bay area photographers who post there, and they might be able to connect you with models they have used.
Overall, the talent pool might be broken down as follows:
1. people on the street, mall, etc.
2. people found through local (nearest larger city) newspaper ads
3. people found via art departments at nearby colleges,
4. people found via the Web (model "directories" like OMP, photo forums, etc.)
5. people found through conventional model agencies.
Each group requires a somewhat different approach, and may be looking for different levels of "validation" of the photographer's credentials and objectives. Remember, while your objectives may be straightforward, there are plenty of predators floating around. Thus, you should be prepared to demonstrate that you're not one of those.
Expected pay scales also vary widely. Art models who pose for drawing and painting classes are usually the most realistic in their expectations. In contrast, Web-based models often have inflated expectations, as they are often accustomed to booking with amateur "glamour" photographers with deep pockets. Those who have worked with other fineart/figure photographers, however, will usually be more realistic, and more amenable to a reduced "day rate".
While conventional agency models are probably the most reliable, they are also the least likely to take figure assignments, as the agencies tend not to want their models posing nude. Web-based models can either be quite reliable (e.g. show up for the shoot, sometimes on time) or complete flakes. Check references, and lean toward those who have established good reputations with other photographers.
I'd also suggest making sure that your expectations for the shoot and all financial aspects be clearly communicated and agreed upon in advance of finalizing the booking. Make sure they understand what you are willing to pay for their time, the amount of any travel compensation, and any other details. Also, make sure that they are willing to sign a standard model release, and are prepared to provide proof of age, etc.
You might also consider having a professional make-up artist (MUA) present at the shoot. While most models can do a fair job with make-up, a pro can make the difference between OK images and great ones. An excellent place to make contact with MUAs is: