How about a 144 grain collar button or 146 grain round ball?
There are still molds around for the 193 grain 455 Webley (can be sized to .457").
There are 210 grain molds around and 250 and 255 grain Colt bullets can be cast and sized to .457".
The 250 grain Barnes XFN is the lightest non-cast production bullet I know of, yet it is expensive.
There are several 300 grain cast bullets available that are inexpensive.
A mold maker could make molds for bullets for many weights.
