Thanks to Bridget for sending this recommendation: 

'I love shopping at Good Health Natural Foods in Hanover, Ma. They have great dairy free selections and all the employees are really helpful! They know that foods that contain casein aren't safe."

It seems they actually have two locations, and they also cater quite a bit to gluten-free consumers:

1627 Hancock Street
Quincy, MA.  02169
(617) 773-4925 

and

219 Columbia Road (Rte 53)
Hanover, MA 02339
(781) 826-0808

Website: http://www.goodhealthnaturalfood.com/