Does one have to make a sheyanu on a brand new silver kos? If one buys it from Hadad brothers (A company that makes silver kosos in Israel-bnei brak) is tevilos kelim necessary? Can this be purchased during sefira?
This can be purchased during the sefirah.
If it is a nice kiddush cup, which brings its purchaser joy, the Shehecheyahu berachah should be recited.
Tevilah is not required, unless the cup is produced entirely by non-Jews, and Hadad only import it.
In general, Hadad is known as a manufacturer of silverware, and tevilah will therefore not be required.