it's really easy to pull the cluster out and change bulbs.
I think there's approximately 4-6 screws you have to take out. I haven't done it in a little while, so I can't recall the exact locations of each, but believe me, it's easy as pie.
a Haynes manual might also be useful to have while you attempt this.
as far as finding replacement bulbs, you're going to have to either hit up a junkyard or go to your local ford dealership. I tried to find the bulbs in stores other than the dealership, but with no luck.
I think I bought a bag of 6 bulbs through the dealer at a reasonable price.
when you take the bulbs out, they just need half a turn, and then you pull towards you. Very very simple.