Home Depot almost always has 'Double Take Scarlet' - a really nice Proven Winners trademarked double flowered vivid scarlet Chaenomeles. It is a medium size, wider than tall but not a dwarf flowering quince. Growth habit like 'Toyo Nishiki' which means it is winter hardy in the ground in Iowa, depending on your local microclimate, might be winter hardy in a pot in Iowa. Flowers of 'Double Take Scarlet' are very similar to 'Iwai Nishiki'.
And to echo BVF - Evergreen Gardenworks has a whole long list of flowering quince cultivars. The most vivid reds are supposed to be 'Kuro' and 'Kurokoji' . I had 'Kuro' at one time, and the flowers were outstanding, incredible velvet red. Of the dwarfs 'Embers' and 'Hime' are excellent alternatives to the overpriced 'Chojubai', their only fault is that they will not get the corky bark that 'Chojubai' develops at somewhere around 25 to 45 years old. The dwarfs might not be as winter hardy as the larger size cultivars, but they are certainly hardy through zone 6. In a pot will need temperature protection in winter.
If you want something larger than starters, contact Brent at Evergreen by email, he frequently will have a small number of larger sizes that he will make available on request.