First, have you tried searching without restrictions? When I put in "dinner" for October 5, 2011 with 5 guests, the system gave me 57 restaurants with availability with a wide range of times (from 4:05 to late, but definitely some 5, 6, 7 pm times). It will be harder to get some types of reservations (CRT springs to mind, and is one of the 16 restaurants listed without dinner availability that day), but it looks like you'll be able to get something.
Second, keep looking! As you may have noticed on these boards, people often change their plans. As they do, reservations may open up. Maybe book the later times and then keep trying to change them to earlier.
Third, have you considered looking for lunch time TS meals? Or early dinners? We often enjoy the break in the day that a TS lunch provides, and then just do CS for dinner. I know that's not as good a value on the dining plan, but it still beats not using TS credits because you couldn't get reservations, or falling asleep over dinner.
Fourth, have you tried looking at the resorts or Downtown Disney? The monorail resorts (and Fort Wilderness) are good bets for a MK day, AKL has a bunch of highly-regarded restaurants if you're in AK, and the Boardwalk, BC, and YC have a ton of great places to eat near Epcot and DHS.
If you're still having trouble by the time you get to WDW, I'd check at the concierge desk of your hotel when you check in to see if they can sort something out for you. There's also always the walk-up option, but that's risky and will probably entail a long wait even if you luck out.