"Pricegrabber":http://www.pricegrabber.com/search_getprod.php/masterid=3494931/sort_type=bottomline has them listed and the best merchant looks like "Fogdog":http://www.fogdog.com/product/index.jsp?productId=1392867 but they only have a few sizes.
The best source seems to be "Zappos":http://www.zappos.com/n/es/d/722049466/order_by/name_asc/page/4.html which has a big variety of New Balance but they are $65, the list price.
We used to use "Road Runner":http://www.roadrunnersports.com/cgi-bin/rrs/rrs/rrBrandShopSearch.jsp?brand=New%20Balance&dept=Footwear&gender=2&BV_SessionID=@@@@0482395163.1125874029@@@@&BV_EngineID=dgaddehkgldkkbelgcgecfefdgf.0 but they seem to have stocked out of many models. They do have a KJ718 which looks the successor to the KJ717 at just $45 compared with $65 list.
"Shoebuy":http://shoebuy.com/sb/s.jsp?&Brand=New+Balance&Dept=Child&Profile=2&Req=prof&b=3&b0=0.82905&b1=1.4&b2=37.76834&scrc=-1&Page=1 is the other source. They stock the newer "KJ718s":http://www.zappos.com/n/p/dp/3535169/c/1416/g/kids/s/Y_4096.html at $60 and the KJ766s rather than the 717s and the 745s that Calvin and Alex like. I've bought from them before and these are $50 and there are often sales and discounts.
I suspect that these are just small updates but have not tried them in store to know