>>9388339>tl;dr I'd say this one with the bullet knights skin belly https://en.kotobukiya.co.jp/product/product-0000003770/The prego bellies are for the megami device line of MODEL KITS, which has 4 different skin colors named A, B, C & D; however, there are only bellies for skin colors A, B, & D so you'll want a kit with any of those colors, pic rel shows MOST of the kits (lacking some new ones) and their respective skin colors for reference.
You'll also want a kit that has one or several lewd expressions to go along with the belly like the one in the link above.
Also, the megami device line has a crossover with alice gear (the bottom row of models in pic rel), but most have a custom skin color different from any of A - D, so watch out for that too.
Finally, for reference, in the image with the preggo bellies some posts above, asra skin is skin color A, bullet knights skin is skin color B, and dark skin is skin color D.
