For what it's worth, I too use Model Mayhem occasionally and agree that as long as you manage your own expectations and do your diligence it can be a useful tool. I'm a hobbyist, so if it takes months to coordinate schedules with a model, or if I have a low hit to miss/flake ratio, so be it (managing my expectation). I will say that every shoot I've actually had with someone from MM (that includes hair/makeup artists as well as models) has gone off splendidly.
I don't know you, so I'm just assuming from your original post that your either a photography student or at least taking a photography class. With that in mind there are three useful paths I'd suggest:
1) Search the models in your area, sorting by newest listed first. They are most likely to be willing to work for trade to build their portfolios. The downside is that they're also more likely to have little to no experience in actually modeling (versus just looking pretty) so might need more direction from you. They tend to be hobbyists and you might have a high no-answer or flake rate, so it's your call if that fits into your schedule to fit them in this semester. If you're just looking to mess around and try things out, this might be your best bet. Often you messing around will get them better shots than are currently in their intro portfolio.
2) Peruse the profiles of models with more experience. Sometimes even more established models are willing to shoot the occasional TF shoot if you can bring something they need to their portfolio - and being able to say you're a real photography student gives you credibility that a hobbyist such as myself doesn't always get. If you have a real cool concept and want to be able to focus on the technical details more than on directing the model, this may be the route to go.
3) Pay for a real model. I don't know what sort of budget you may have, but again play the photography student card. There are plenty of "models" asking for exorbitant rates, but there are also plenty of models with reasonable rates, and some who give discounts to students (whether due to altruism or to an assumption of the quality they'll receive I don't know - but then who cares if the bottom line works for you?). These tend to be the most reliable and require the least direction.
Again, if you do your research, check their references, and trust your instincts, you can weed out most of the flakes. Also presenting yourself in a professional manner (contacting with as many specifics as you can, not just "Hey, wanna shoot sometime?") helps.
FYI, I tried searching for your MM screen name and couldn't find you. Not stalking you, just curious to see the selection of models in your area. Has your account been activated yet?