soft metal alloy

There are several formulas of very soft, low T melting Bi-Sn alloys. Look for "Wood's metal" with google. Can be prepared in workshop, but be careful: never in a platinum crucible!...

J.J.

You find lists of soft alloys when looking for:

"fusible alloys" "low melting point alloys"

either with google, or in any edition of the "Handbook of chemistry and physics"

J.J.

Sodium can be easily cut with a knife. Did you require any other properties?

Uhmm, don't you see potential problems with suggesting Sodium for the intended application?

If the original poster had any other restrictions on the material, he should have mentioned them. For all we know, he might like the patina which forms on a raw sodium surface.