Have you asked WHY he never got you a ring? The majority of both men and women understand this is accepted custom to do.
A ring does not need to be large or expensive, but you should still have one, unless you chose not to.
Does he not have the money? Does he not think a ring is worth spending money on? Is he not a fan of tradtion/customs/conformity?
On the positive side, you ARE married, and a ring is nothing more than a material object. Provided you are happy with the relationship in general, this may not be such a big deal.
BUT if money is NOT an issue, and you want a ring, then I think you should ask that your husband buy you one. That is the traditional role of the groom/husband.
Tell him that you don't feel like a "real wife" or whole without it. I'm sure he wants to make you happy. You could also tell him that men have asked you out for dates, because they had no idea you were married! How would they know?!! Most guys look for a ring! That should do the trick!
Good luck!
P.S. If all else fails, then yes, you can buy yourself a ring. But in all honesty, if he will not spend $200 (provided you have the money) on a simple wedding band to make you happy, you might have to ask how good of a husband he really is.