Many people gave you valid suggestions to address your problem. Sometimes you need to think laterally - your answer may not be in travelling the shortest distance! I don't know of any serial/parallel memories - even fifos. You can, however, implement one in a fpga. My suggestion was to use a ethernet chip - which funnily enough does what you want, in a roundabout way. It is parallel in/out, has ram with a serial interface at 10/100Mbit/s. It will be most likely, faster, chepaer and quicker to prototype than using a fpga.