Western Design Center at
http://www.westerndesigncenter.com/wdc/ makes them in 14MHz and with more instructions than other 65c02's you've probably seen. These 65c02's have the added signals, bus enable (BE) input on pin 36 of the DIP, memory-lock (ML\) output on pin 5 of the DIP, and vector-pull (VP\) output on pin 1 of the DIP. You don't have to use them, but they make it easier to implement things like a multi-processor system, DMA, and hardware interrupt vectoring. They have the data sheets and programming manual on their website, and you can order directly from them or from Mike Naberezny here who runs 6502.org.
But if you're making a new SBC or can make slight modifications, I would recommend going to a 65816 which has 16-bit extensions to the instructions and new capabilities that open up a load of new freedoms and make a lot of programming tasks easier and more efficient. Some things it can do were nearly impossible on the '02, like relocatable code, or much more limited on the '02, like multitasking. [
Edit, 5/15/14: I posted an article on simple methods of doing multitasking without a multitasking OS, at
http://wilsonminesco.com/multitask/index.html.] Don't let the 16MB address capability and 16-bit-capable registers intimidate you though. You can still use it like a supercharged 6502 in a 64KB address range. If you're making an SBC, you can arrange a few jumpers so the board will accept either the 65c02 or 65816.