You might try looking around
on ebay for raw conrod forgings that are a suitable size. I'm sure you can find someone that sells raw alloy steel conrod forgings if you keep looking. Try some US aftermarket/race component manufacturers like Crower, Manley, Lunati or Eagle Specialty. Even if they won't sell you forgings they can probably tell the name of someone who will.
If you want to purchase some alloy steel bar, give a
large US supplier like EMJ metals a call. I don't believe there is currently US restrictions on exporting non-proprietary alloy steel raw materials to Columbia, but you should
check with them to make sure.
If you decide to use wrought steel bar, I'd recommend spending a bit extra for vacuum melt quality 4340 VAR (AMS 6414). Just remember that high-performance steel conrods typically start with a hot die forged blank, that then gets 100% machined all over to remove the hot forged surface material. You'll probably need to do the same if you start with hot rolled bar stock.
Lastly, don't forget you will also need a source for high strength (Al bronze or similar) bushing stock, high strength bolts, shot peening, heat treating, etc.
Good luck with your project.