I'm a lefty that shoots rifles right handed, but your dilemma is valid, but as far as manufacturers go, still an extreme minority. 
There are a few, but it will make your rifle unique, and my only advice would be to get specific lefty spare parts to keep in your stockpile.
If the SHTF, the right handed parts will go, but the lefty stuff will go even faster.
You know how hard I had to look for "left-handed" ammo? 
First off, I got some left handed ammo for ya'. The only problem is it tends to pull to the right. lol
Anyhow, on the more serious aspect of your post, the SHTF and ability to find and get parts, whether they be for a left or right handed AR, I can completely agree to and with.
The fortunate, actually it's unfortunate because trust me, I'd rather be shooting da' crap out of it, but the thing is, I don't do a lot of shooting because where I'm at in Illinois there isn't many places for me to go to. For rifle I have to go into Wisconsin. So by the time and if and or when S may HTF, I don't think anything will be so worn that I'll have to replace anything. But I have gotten some stuff but it wasn't because of SHTF, but just because. But if, or rather when I convert this puppy to piston, some of those items will no longer be used or needed. That is unless I convert it back to direct impingement/gas or pick up another AR.
But the one thing I do plan on getting myself is an extra left handed bolt carrier assembly, obviously bolt included. Other then that, I'm not worried about much when it comes to SHTF or anything else.
And I suppose, FWIW, besides not being able to shoot much, the cost and availability, or lack there of, of defensive ammo, and ammo in general, is what also limits and prohibits my ability to go shooting often.
And trust me, if I had my choice I'd wear my Ar ut and anything else I have or may have, in a heart beat.