Finding the crystal shouldn't be a problem, you've probably already got a load at home.
The crystal of first cheap plastic clock I opened worked immediately and I found loads of others on all kinds of old boards/cards.
Assuming I have those around me is a mistake. I don't, the only thing I have with that crystal is my Casio, and apart from being my favorite watch, is still working. Spare parts are so scarce around here I can't put a mega16 running because I don't have the capacitors for the crystal. I know, I know, I'm lazy. I'll be headed to my favorite electronics shop next week so I may find something.
[quote author=Geek 2.0 link=topic=56908.msg408912#msg408912 date=1301409372]
What if I didn't run at 16 MHz? This project idea is actually for a custom board running the arduino bootloader, and/or a breadboard arduino (I don't really use my Duemilanove anymore).
I'm curious to see if we could get this to work...
It all boils down on what you are using. If you change the fuses on the mega168 or 328 and use the 8MHz internal clock, you can have the TOSC pins for the real time clock. Or, if you are using another chip, you may be able to get away with both. For example, if you are using the ATmega16, 32, 324 or 644 (they all share the same pinout), you can have an external crystal and also the 32768Hz crystal for the RTC. (the TOSC pins are PC6, 7)
I was actually test my code on the ATmega16 mentioned previously, so I guess all I need is the crystal and two 22pF capacitors. LOL