hardcore misery, ganda ng proto board, linis ng gawa. sa mga lumang atx psu siguro pwede ka makakuha ng filter.
off sa topic pero share ko lang kung makakatulong. try to search emi reduction technique on the net, secondary resort nalang and additional filter but it doesn't mean di na kelangan. Try to suppress where the emi came from. good layout practice will lessen emi effect. for example, power loop must be keep as small as possible. try to lessen the dv/dt or di/dt or the slew rate of the voltage and current and try to lower the peaks. If your are using flyback converter, try to operate at continues mode for it will lessen the current peak and will further reduce the emi not to mention the possible efficiency gain. in driving the FET try to use higher resistance value, it will slow down a little the dv/dt but off couse the penalty on efficiency. if the power fet and rectifier waveforms have oscillations and ringing, try to remove is or lessen a little using snubbers ckt.
these are just some thought and good luck on your next design.