Personally, I start out looking at 2 years in terms of correlation timeframes and mining possible pairs. And I use common sense to further pare down the non-sensical stuff ( like rubber vs gold ).
If you do not have access to a Bloomberg terminal, I would highly recommend CSI over MRCI. Also, really check these results using chart overlays - don't trust anyone's data at face value. Finally, use some short charting timeframe intervals with your overlays to check for viability, wandering, and cointegration-like tendencies. If the charts seem promising, I would then spend at least a few weeks looking at the product order books (market ladders are best) placed side-by-side on your execution platform.
You should also expect to ferret through MANY of these possible combinations before you find something that inspires enough confidence to trade it live. Two of the most prominent strategies for these combinations are lead-lag and synthetic intramarket spreads.
Good hunting and best of luck. This is indeed a very worthwhile endeavor if you have the drive and determination to put in the work. No free money anywhere - it all takes sweat equity and working smart and not just hard.