integer frequency division
Use a phase locked loop. 

It can multiply an input frequency by an integer quite easily. For instance, 800 Hz could be simply converted to 5600 Hz. Dividing this by 8 then gives you 700 Hz. The trick to obtaining all the frequencies you need is finding a frequency that can be divided by an integer to produce 300Hz, 500Hz and 700Hz. I believe this would be 84kHz.

If you divided this by 105 you get 800Hz so, construct a phase locked loop with input frequency of 800 Hz and output frequency 105 times higher



In the above diagram, REF is 800Hz and the output of the VCO (voltage controlled oscillator) is 84 kHz. The divider is a divide-by-105.