Plastic flatbed knitting machines are mostly mid-gauge or bulky but there are some standard gauge machines as well. They were manufactured by Japanese and European companies (Singer, Studio, Silver Reed, Brother, Phildar, Passap, etc.) Some are still being manufactured and are very popular among machine knitters. Below is the list of the machines I personally had knitted on.
Singer HK100, bulky, basic
Brother KH341, standard, manual/basic, foldable
KnitKing Simple Seven, mid-gauge, basic
Brother KX350, mid-gauge, basic
Brother KX355, 7 mm, basic/manual, plastic bed
Brother KH360, 4.5/9 mm, basic/manual, plastic bed
Brother KH370, 4.5/9 mm, basic/manual, plastic bed
Brother KH390, 4.5/9 mm, basic/manual, plastic bed
Brother KH395, 4.5/9 mm, basic/manual, plastic bed
Brother KH400, 4.5/9 mm, basic/manual, plastic bed