You may want to start by giving this a read. While it is a three phase circuit I would imagine two such circuits could be built and the input clock to the second circuit shifted. Another method might be the use of a pair of small mechanically driven 3 phase synchros or small 3 phase PM motors. I assume you want 60 degrees phase lead / lag?
A six-bit serial shift register would produce 6 phase square wave with 60 degree phase. It's a matter of shaping the square wave into a sine, then amplify the resultant signal.
A switched cap filter like the MAX291/292/295/296 can take a square wave and make a sign by removing the harmonics. The filters need a clock of 50 or 100x the frequency of what you want. Make 1.5mhz and using a counter divided by 100 to get 15khz. Now feed the 1.5mhz into the clock of the filter and the 15khz into the input. You will get a very clean 15khz sign wave out. The 100 (or 50) does not need to be exact. You should use a number that is dividable by 6, more on that later, so use 102 or 96.
Using the counter create 6 square waves in phase like the the sign waves you want. Use ideas form the link above to get started.
You will need 6 low pass filters like the MAX291 all having the same 1.5mhz clock. Each filter will have a square wave input 1/6 out of phase.
No I am not going to draw a schematic. I hope you can use some of the ideas. Look for data sheets and application notes on parts like the MAX291.