Town officials have drafted a request for proposals seeking to find a new tenant for the Bank Building, the first floor of which will be vacant when Eastern Bank moves later this year. The bank occupies the first floor of the building at the corner of Main and Centre streets that houses several town departments on the upper floors. The town rents the space out for about $38,000 a year. “Hopefully we’ll be able to drum up some interest,’’ Town Manager Charles Cristello said at Tuesday’s selectmen’s meeting. Town officials said they tried to persuade Eastern Bank to stay, but the bank will move the branch to Lakeville. Other changes are in the wind in the downtown area with the decision by Mayflower Bank — just across the street from Eastern Bank — to leave its South Main Street location. That storefront will become a Rockland Trust branch.