Rings for BSA Supersport five

[nbmonte]

I'm trying to add a scope to an old BSA supersport five I've got and can't find any rings to fit. The dovetail on the receiver measures around 16mm. I've tried an old pair I had and they gripped, but not well enough. I picked up a pair of millets that looked wide enough to try today, but they were made for a flat top, which I didn't notice when I grabbed them. I tried searching both here and google, but I'm still not sure on what would work. Any help is appreciated.