My default is to go through http://www.mouser.com/
. Order spare parts for this and/or other projects, as parts are cheap, shipping is not. You could also try ebay for parts, but likely you'll source them from China. For resistors and caps, you should be able to keep it here in the US. Third option is to go to a local Radio Shack if you need them right this minute, but their selection will be vastly limited.
For resistors, I would go with just your typical 1/4 watt metal oxide resistor. Tolerance shouldn't be too critical, so look into a 5 or 10%.
Now, for the capacitors, dare I open the flood gates? Two camps for these little devices. 1) Capacitance is capacitance and any type (i.e. film, ceramic, aluminum electrolytic, etc.) will be fine. 2) to get that MOJO you must use Sprague Orange drops and/or the ole Bumblebee paper-in-oil capacitors.
Personally, I fall into camp 1 and this keeps my tone and wallet happy. To each his own.
Hope this helps, best of luck.