Well...it ain't mama's, but it sure is good:
New York City is current ground zero for authentic Japanese, thanks to the influx of wacky Japanese kids to the east village. Village Yokocho, at 9th and 3rd Ave has more
nomiya and street-style of cuisine (various forms of skewered dishes, from quail egg to shrimp to viscera, etc), along with grill tables for the Japanese version of Korean-style fun. Down the street is a shop that has takoyaki and okonomiyaki. Sobaya is just around the corner. There's a Japanese bakery downstairs that does decent cream-an buns. (Alas, they don't compare to Brookline, MA's Japonais' baked goods).
Atlanta, shockingly, also has an array of specialty Japanese restaurants -- something about the large number of corporate headquarters in the area make it a stop on the Japanese expat train. Joli Kobe has a Japanese Bakery (fluffy breads, cream-an buns, less sweet pastries), and there is a Yakitori-focused restaurant called Yakitori Jinbei. I used to eat in a restaurant there called Yokohama - the sushi chefs really were from Yokohama. We would chat in Japanese and they'd always bring me a little homey dish or two. They made excellent home-style food there, but I can't vouch for it now as that was over 10 years ago.
My longtime favorite mama-style restaurant (with the usual sushi, sukiyaki, etc. thrown in) was a place in Boston that no longer exists. Tatsukichi, when it first opened in the 80s, was an authentic Japanese experience. They specialized in
kushi katsu (friend skewered foods) and had marvelous
niimono (steamed/boiled dishes). It changed pretty rapidly, and eventually just died a sad, lonely death.
In Cambridge, MA there is the Porter Exchange, a rag-tag lineup of street food shops that include a ramenya, a sobaya, a sushiya, a
kissaten (a 'Western Style' restaurant where you can get coffee, doria - a mac n cheese type rice dish, and white bread sandwiches), a tempuraya, and another space that seems to change every few years. The food is average, but fun -- not too different from the food court at Mitsuwa except in quality (better).
In LA I've had a few tasty meals, too. Mishima had a great selection of street food -- curry, cold noodles, desserts. Curry is one of my favorite Japanese home meals, and thank goodness there are now special 'artisan' curries on the market so I no longer have to use the strange hydrogenated blocks of House curry anymore. If you haven't had Japanese curry before, it really is the comfort food of all comfort foods and is as common there as mac n cheese is here. They serve it at Tokyo Disneyland, in cafeterias, at the airport, at train stations. There is nothing like
eki-ben, short for
eki-bento, or the very commercial but very satisfying bento breakfast, lunches, and dinners you can buy at a train station. If I could find
eki ben at a rest stop in the US I'd be a very happy traveler.
In general, Japanese restaurants in Japan are very focused. You won't be able to get sukiyaki at a sobaya, or soba at a ramenya. Nomiya have booze-centric snacks (grilled fish, cold dishes, finger food etc). Sushi shows up in sushi restaurants, and tofu gets its own treatment in special tofu restaurants.
When I want homestyle, I cook it myself. For years I cooked nothing but. I have this fantastic cookbook I purchased in 1997 that is the ultimate home-style beginner's guide. It is called "A guide to Popular Japanese-Style Meals" or
washoku no teiban, written by the Chief Steward of the Mitsui OSK ship line. It is bilingual and contains the basics of home cooking. There is no sushi in it, but it is food that you could eat everyday, morning noon and night. I'd recommend a homestyle illustrated cookbook for those wanting to dig into something outside the Japanese restaurant cannon.
One thing I miss the most is Japanese variants on French Pastry. The Japanese do magnificent work with pastry and their product is both smaller and less sweet than US and European counterparts. They have performed extremely well in the Pastry Olympics - deservedly so. Japonaise in Brookline used to be quite good in the '80s but isn't so impressive nowadays. There are chain bakeries in New York, but they lack the subtlety of the small artisan bakeries in Japan.
So I guess my final recommendation is that if you really want to learn about great Japanese homestyle cooking, take yourself to Mitsuwa, get yourself a homestyle cookbook, and teach yourself. It really is different. And not difficult.