If do you wanna a rear-fanged one, maybe you may enter in confront with problems with food and you should think about it. Althought aglyphous, opheodrys is a good candidate as it eats insects. On another point, Leptodeira is an almost anuran-eater specialist as many opisthoglyphous species. I am not intended to make merchandising, but while surfing I found a classified of LLL reptile supply, maybe they got what you need. I dont know about it feed needs, but I think you would like the keelback snake. It looks like what you expects.
classified link