Other than the Phillips SMD one, the only other I2C uart i managed to find is the BL233 at http://www.i2cchip.com/#Host%20Adaptors. I suspect that's just a custom programmed PIC. Considering the relatively slow speed of I2C and MIDI, would the best solution be to use something like a PIC 12F629? It's 8-pin (6 I/O), has 1024 words of Flash program space and an internal 4MHz oscillator. With no internal uart of any sort, you'd have to big-bang both the I2C and MIDI, but it would be the most flexible solution.