I have what's referred to as hyperlordosis, which is an exaggerated curvature in the spine. I'm not 100% sure, but I believe the curvature prevents my breath from fully moving in and out.

Neither my chest or belly moves in and out when I breath. In fact, it's like I don't breath at all. I literally cannot find the breath and this makes concentration meditation almost impossible.

Does anyone else have this problem or know how to deal with it? I suspect this is not a common issue.

You are alive, so air does move in and out, and that movement happens only because your diaphragm is moving up and down or your ribs are expanding and contracting.  Whatever the mechanical mechanism that's drawing air in and forcing it out is observable/sensible, and that observation will lead to other observations in an expanding fashion to the whole body.  

It's not unheard of, to find it difficult to notice sensations of the breath.  You can put your hand on your abdomon to increase awarenss of breath, which might lead to noticing the more subtle feelings. You get to use any part of the sensorium for the practice.  I mean, maybe what you feel is the belly rubbing against the wasteline of whatever you're wearing and that sensation changes a bit as you breath, or maybe a sensation of the rush of cool air into the lungs turns into a wave of very subtle tingling into the abdomen.  Or maybe you can feel your heart pulse in the abdomen and some aspect of that feeling changes as you breath in and out. Maybe there is a generalized awareness of the pressure of clothing or room air at the abdomen and that sensation changes as you breath in and out.  I'd give it lots of hours before you give up on the abdomen.

But if you do get to the quit point.... use your intellect to suss out how the heck that air is moving in and out of your body, then look for sensations that support your theory.  Maybe the nerves around your ribs, or near your diaphragm are sending signals that you have not noticed.  

Some people find sensations of breath at the entry of the nose an easier target.  I do.  One of my teachers in the past said stay away from using the nose sensations as a object becase it's more likely to lead to distracting absorptions, but I think that's a feature, not a bug.

I like the advise, "start with what is reliably noticeable", and expect that your ability to notice will change over time, and notice *that*.

You might try changing your meditation posture. I have a mild form of what you describe, and I cannot comfortably sit on a cushion with a straight spine, partly because my diaphragm is constricted by my tight abs and won't freely move. So I sit in a big, comfortable chair in a slightly slumped position but with my head erect. Much easier for the belly to move in and out that way. I can sit for an hour with little discomfort.