You'll need to get a pair of quick release axles and a pair of quick releases. The axles will have the same threading but be shorter (or you cut them to fit) so they are just slightly shorter than the distance between the outside surfaces of the track stay ends. Bicycle Research, I believe, has a huge number of such axles for around $12/axle -- just get the right diameter, threading, and length. Theirs are at least as good as the original ones that come in any hubs made; the quality is great. As for quick releases, on a fixed gear you need good ones, and Shimano Dura Ace are usually considered the best, followed closely by Salsa. Stay away from alloy or titanium QR's; you want sturdiness here. Cheap QR's tend not to grab as well and you need all the clamping power you can get. The front obviously isn't as big an issue, but you haven't solved your problem if you only address one wheel (if you have to remove a wheel every day to bring the bike into your apartment, your car, your workplace, that's a different matter).
If you are just riding the bike, you should be fine with quick releases. If you skid, you'll find you will still pull your rear wheel loose, and you also will tend to bend the hollow quick release axle over time. In other words, if you are into that kind of move on your bike, stick with regular nutted axles. Quick releases simply don't hold as well and the strength of the axle is compromised.