Most scale manufacturers are using the RS-232 serial interface to send data to a computer and I don't know of any iOS app that will talk with that interface.
For the Mac, which also lacks a serial interface, you should look at the Postal scales that are made by Mettler Toledo. They have both the RS-232 and a USB interfaces with a range of sizes. I've found the PS15 model will work with a USB interface but have needed the interfacing code that Andy Knasinski from NRG Soft wrote in order to make it write the weights to an FMP database on my Mac.
A reliable supplier for these scales is AMS in Macomb, IL. Ask for Scott Wisslead.Scott <firstname.lastname@example.org>