Where can I purchase an airport time capsule power cord?

Amazon.com: OMNIHIL (8FT Long) AC Power Cord for Apple Airport Extreme / Time Capsule - 2TB / 3TB and Express Power Supp…

If you have a Frys close by, they will have this type of cord as well. Ask for a Figure 8 power cord. Take the Time Capsule along to make sure that the cord will fit correctly.

Pretty much any electrical or big electronics store will sell the standard fig 8 power cable.. it is stock standard.. but inevitably black colour.

Apple store AFAIK do not sell replacement cables.. which is a shame because they are very good quality and extra flexible. Plus it is white.. like new driven snow.

If you have a store nearby they might have a spare laying around.

A good source of cords btw is second hand airport extreme.. cheap old one is fine.. Apple used the same cable for many years.. in the earlier model plugged into external power supply.

you may even have one around, my old playstation 2 use the same cable as do an old cd player and an ancient portable radio in the garage. it's an industrial std.