3a is a pistol only rating.
Technically there is no official 3+ rating.
There is only 3 or 4 for rifle plates. 3+ is just a way of showing some plates that can stop rifle rounds at a higher velocity than the normal level 3 rating. They still won't stop the AP rounds level 4 will.
Looks like there's still some options left depending on size and plate coating:
https://www.midwayusa.com/ar500-armor/b?bid=1098124
Can't vouch for them as I've never used them but seem to have good reviews online.
Edit: also free shipping on armor if you order $100+
Seems these have somewhat irregular roll marks. May also have other cosmetic issues. Not a big deal to me but it's not being sold as a blemish which is a bit disingenuous of Colt I think.
Couple of places have Magtech 77gr 556 for less than $.60/round. Seems like a good price for you longer range shooters:
http://www.sgammo.com/product/223-556mm-ammo/1000-round-case-556x45-otm-77-grain-smk-hollow-point-magtech-first-defense-sn...
You want PSA? Grab their CHF M4 kit + a $50 Anderson stripped lower:
http://palmettostatearmory.com/psa-16-carbine-length-chf-m4-5-56-1-7-rifle-kit.html
Get an FN nice barrel there!
GT was always preferred because they kept the lacquer and case sealant when Wolf and others went to poly with no sealant.
I think the Monarch brand that Academy stocks might be made by Barnaul?