Cacti will be difficult here on the east coast. I have opuntia, cylindropuntia and hardy agave ( harvardiana, parryi and ovatifolia )that go unprotected. But other barrel and columner cacti along with less hardy agave are covered by pots during winter. Also my soil is amended with compost and peagravel for drainage. then the plant is placed in 100% gravel above grade to keep the roots dry in winter. You can find several hardy cacti and agaves for zone 7. But last year we had 60" of rain on the east coast. So to keep your cacti alive keep them dry in the winter.

I get most of my plants from plants delight nursery, yuccado nursery or high country gardens.

I am not sure where you live and how wet it is there. TRhat is the real killer

High Country Gardens will have some for cold hardy Zones.
http://www.highcountrygardens.com/cacti-succulents

So will Cold Hardy Cactus
http://www.coldhardycactus.com/index.htm

And Intermountain Cactus. They also sell a book "Growing Winter Hardy Cactus in Cold/Wet Climates" by John Spain. They list their cactus in Zones.
http://www.intermountaincactus.com/Intermountain_Cactus/Home.html

Here is a link that might be useful: Cold Hardy Cactus Nursery

I have seen people grow cactus in the Hudson River valley, but they create removable shed roofs to protect the plants from the excess moisture. A southern covered porch is a good thing. The low winter sun gets under but the rain is minimized. I am a Texan so I really don't know squat about cold and wet that you get. I get some but nothing like you guys. . I have seen others cover with a potable greenhouse and lights for heat in Iowa or some place like that. Saw pictures of a thread on here, I think.

If you see people in your neighborhood that are growing them, STOP the car , swallow your shyness and knock on the door and ask them what they are doing. Most gardeners are very open with their knowledge. You might even be gifted with a cutting. That is what I usually do when someone asks me.