There are a couple of ways to get an LED to flash.  The simplest by far is to use a timing chip.   There are two different timing chips that I have used for models.  The 555 timer and the 4060 cmos chip.

For your purpose I think that the 4060 will work because it does a couple of things that will make your life easier.

One it will regulate the voltage in other words, the voltage you feed into the circuit can be higher than what the LED needs and this chip will drop the voltage to a safe level for the LED.  

Second, it will give you many different blink rates off of the same chip.   Each output pin has a multiplier to it.  In other words, one set of outputs would give you that one second blink while another might give you the three second blink. 

The 555 timing chip will not do either of these.  Voltage in equals voltage out, and you will need a seperate timing chip for each led.

I have a brief explanation here:

http://www.scalemodeladdict.com/forum/index.php/topic,712.0.html

In the picture on the link, pins 1-7 and 10-12 are output pins.  You can just connect LED's across those pins and play around until you get the blink rates where you want them.

Both sets of timing chips use a resistor and capacitor in combination to set the timing.  I do explain how I set up my timing on that link.

And more on the 4060 here:

http://www.starshipmodeler.com/tech/cj_blink.htm