No, Weaver does not make a sidemount for either the no.1 or the 4 or 5.
But Williams makes a neat one the SM-70 for the No 1 Mk3 and the
SM-71 for the flatsiders. They are available fro Brownell's and retails
for under $50 with the rings, I think. I haven't installed one yet,
but by the looks, it should be pretty straight forward. But again,
you have to drill & tap, which should be easy.