Past years the specified low quarter was the M206H (Mens) and M210P (Womans) from AAFES. This was also the early guidance for 2017 from the official USMA Parents Page
The Men's model can be found here:
http://shop.aafes.com/shop/Product.aspx?dept_id=3030&PFID=M206H
And Woman's:
http://shop.aafes.com/shop/Product.aspx?PFID=M210P&dept_id=3040
This is the "DLATS Men's/Woman's Military Oxford". DLATS means Defense Logistics Agency Troop Support which means it's a standard issue item.
Normally it's a particular Bates model, (I believe it's the E00968 Mens, E00769 Womans, but would have to confirm). It's also commonly sold in uniform stores, etc.
Any PX/BX can order these, and the fit is almost identical to the "High Gloss" version they normally stock, also known as Chlorfams/corfams, etc. Unlike the high gloss, which are plastic, the leather ones will stretch a bit more, but otherwise are identical and made on the same last.
Or just order from AAFES. Free return envelop if the wrong size, or you can return it at any PX. Candidates cannot order directly from the website as they don't have their ID yet, but there is a number they can call. I have the number from past years, but you'll need to confirm for this year in case it changed.
You'll have a better chance at finding the M206H / M210P at Air Force posts, as they (apparently) are the main service that still wear them.
Note that the AAFES price on the low quarters is under $50, yet you'll pay over $100 in most surplus/uniform stores.
Similar info for boots,,,,,
Bates M-8 (1450)
http://shop.aafes.com/shop/Product.aspx?dept_id=12030&PFID=M417S
Belleville 310
http://shop.aafes.com/shop/Product.aspx?dept_id=12030&PFID=M417R
I note that AAFES does not show the smaller sizes (Woman's) for the M-8 while the 310's are listed down to size 3.
The Khyber was not sold at AAFES, but is the Belleville TR360. It's a lighter weight boot, and can be bought at the Cadet store or ordered by calling them. It's from Belleville's cheaper line, and are Chinese made, so do not expect them to last as long. (Which is also why they are not DLAT boots) But they are also cheaper to purchase, MSRP is less than the AAFES price on the other boots.
Here's the Khyber at Belleville:
http://www.bellevilleboot.com/shop/index.php?l=product_detail&p=67
The 2nd pair issued in past years has been the DLAT hot weather boot listed on the AAFES page.
Dixieland's input on sizes is dead on. The PX & C-store staff indicate it's not uncommon to find 1-2 size reduction over what the candidate thought they wore, and occasionally 3 sizes. And that also that they run true to fit on the brannock foot measuring device if fit by someone who knows how to use/read it.