Of the companies listed here, Tronica is the only one that I have a hard time listing here. I have found Tronica games in several shops in America, but most of the shops are the import type of place, so I have a feeling that Tronica wasn't an American manufacturer, though I'm not sure. If you can shed some light on this, feel free to write!
Grandstand and Lansay games are mostly other companies titles, in some cases renamed, but in all cases with their logos where the other companies logos were. I've seen the Grandstand logo on games from Epoch, Entex, Tomy and a few others. Lansay is primarily Gakken, but I'm sure their talents weren't limited to one company.
Liwaco, Sunwing and Tronica are primarily LCD game makers and their games seem to all be original! Sunwing has a ton of titles that I've seen in the same shaped cases (I wish I still had the pictures) and I've seen several of Tronica's games in the same shaped cases as well. Liwaco seems to break the mold and does a variety of different handhelds in different cases and styles.